Show that $d/dx (a^x) = a^xln a$.












9














Show that
$$
frac{d}{dx} a^x = a^x ln a.
$$



How would I do a proof for this. I can't seem to get it to work anyway I try.



I know that
$$
frac{d}{dx} e^x = e^x.
$$
Does that help me here?










share|cite|improve this question





























    9














    Show that
    $$
    frac{d}{dx} a^x = a^x ln a.
    $$



    How would I do a proof for this. I can't seem to get it to work anyway I try.



    I know that
    $$
    frac{d}{dx} e^x = e^x.
    $$
    Does that help me here?










    share|cite|improve this question



























      9












      9








      9


      2





      Show that
      $$
      frac{d}{dx} a^x = a^x ln a.
      $$



      How would I do a proof for this. I can't seem to get it to work anyway I try.



      I know that
      $$
      frac{d}{dx} e^x = e^x.
      $$
      Does that help me here?










      share|cite|improve this question















      Show that
      $$
      frac{d}{dx} a^x = a^x ln a.
      $$



      How would I do a proof for this. I can't seem to get it to work anyway I try.



      I know that
      $$
      frac{d}{dx} e^x = e^x.
      $$
      Does that help me here?







      calculus






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited May 22 '13 at 3:48









      kahen

      13.2k32554




      13.2k32554










      asked May 22 '13 at 3:25









      1ftw1

      3602615




      3602615






















          7 Answers
          7






          active

          oldest

          votes


















          16














          Hint: $a^x=e^{ln a^x}=e^{xln a}$.






          share|cite|improve this answer





























            5














            Let $f : mathbb{R} to mathbb{R}$ be given by $f(x)=a^x$ and consider the $ln$ function. We can take the composition so that we have:



            $$(lncirc f)(x)=ln (a^x)=xln a$$



            Now, if we take the derivative, on the left hand side we use the chain rule and on the right hand side we differentiate as usual so that we have:



            $$frac{f'(x)}{f(x)}=ln a$$



            Now solving for $f'(x)$ gives $f'(x) = f(x) ln a$ so that $f'(x) = a^x ln a$. This useful technique can be used to take derivatives of other functions: we compose the original function with the inverse and then differentiate on both sides and use the same idea we've used here, this technique can simplify many derivatives and save a lot of time in some situations.






            share|cite|improve this answer































              3














              Hint: Write $y = a^x$ or equivalently $ln y = x ln a$ and use implicit differentiation.






              share|cite|improve this answer





























                1














                enter image description here, the last term, enter image description here, can be explained by L'Hopital's rule, just taking the limits of the numerator and denominator one of each time.






                share|cite|improve this answer





























                  0














                  Here are the steps
                  $$
                  frac{d}{dx} left[a^xright] = frac{d}{dx} left[e^{ln a^x}right]= e^{ln a^x} frac{d}{dx} left[ln a^xright]
                  $$
                  $$
                  = a^x frac{d}{dx} left[xln aright] = a^xleft(ln aright)frac{d}{dx} left[xright]= a^xln a
                  $$






                  share|cite|improve this answer





























                    0














                    $ frac{d}{dx} a^x=$



                    $=d/dx$ $e^{ln (a^x)}=$



                    $=d/dx e^{xln(a)}$ just as you said.



                    Now it's time for chain rule.



                    $f(x)=e^x$



                    $g(x)=x*ln(a)$



                    $a^x= f(g(x))$



                    last comment before I get solving



                    $a=e^{ln(a)}$



                    now let's get it done



                    $d/dx e^{x ln(a)}=$



                    $=e^{x*ln(a)} d/dx (x ln(a))=$ (by chain rule)



                    $=e^{x ln(a)} * ln(a)$



                    and that is the solution. Wait it doesnt look correct --> we should do some algebra!



                    Show for yourself that



                    $e^{x*ln(a)}=( e^{ln(a)} )^x$ but as we said that $a = e^{ln(a)}$ so $( e^{ln(a)} )^x$ actually equals $a^x$ and of course $e^{x*ln(a)}$ equals a^x



                    With what we just said you can see that $e^{x * ln(a)} ln(a)$ equals $a^x ln(a)$ or



                    $$d/dx a^x = a^x ln(a)$$






                    share|cite|improve this answer



















                    • 1




                      Use TeX while typing math symbols
                      – supremum
                      Jan 5 '15 at 17:59










                    • For help, see this FAQ entry about $LaTeX$ on Math.SE.
                      – Ruslan
                      Jan 5 '15 at 18:43





















                    -1














                    Let $y = a^x$



                    Then taking log on both side to the base $e$



                    We have;



                    $ ln y = ln a^x$



                    $ ln y = xcdot ln a$



                    Taking derivative with respect to $x$;



                    $frac d{dx} ln y = frac d{dx} xcdot ln a$



                    (I have applied chain rule here>>)



                    $ frac 1y frac{dy}{dx} = ln a + 0$



                    $ frac {dy}{dx} = ycdot ln a$



                    We know $y= a^x$



                    So, $frac {dy}{dx} = a^x ln a$



                    Hope it was easier than other methodologies used to derive it!






                    share|cite|improve this answer























                    • The question is five years old and your answer adds nothing new to the already existing answers.
                      – José Carlos Santos
                      Nov 21 '18 at 9:39











                    Your Answer





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                    7 Answers
                    7






                    active

                    oldest

                    votes








                    7 Answers
                    7






                    active

                    oldest

                    votes









                    active

                    oldest

                    votes






                    active

                    oldest

                    votes









                    16














                    Hint: $a^x=e^{ln a^x}=e^{xln a}$.






                    share|cite|improve this answer


























                      16














                      Hint: $a^x=e^{ln a^x}=e^{xln a}$.






                      share|cite|improve this answer
























                        16












                        16








                        16






                        Hint: $a^x=e^{ln a^x}=e^{xln a}$.






                        share|cite|improve this answer












                        Hint: $a^x=e^{ln a^x}=e^{xln a}$.







                        share|cite|improve this answer












                        share|cite|improve this answer



                        share|cite|improve this answer










                        answered May 22 '13 at 3:38









                        A. Chu

                        6,98583283




                        6,98583283























                            5














                            Let $f : mathbb{R} to mathbb{R}$ be given by $f(x)=a^x$ and consider the $ln$ function. We can take the composition so that we have:



                            $$(lncirc f)(x)=ln (a^x)=xln a$$



                            Now, if we take the derivative, on the left hand side we use the chain rule and on the right hand side we differentiate as usual so that we have:



                            $$frac{f'(x)}{f(x)}=ln a$$



                            Now solving for $f'(x)$ gives $f'(x) = f(x) ln a$ so that $f'(x) = a^x ln a$. This useful technique can be used to take derivatives of other functions: we compose the original function with the inverse and then differentiate on both sides and use the same idea we've used here, this technique can simplify many derivatives and save a lot of time in some situations.






                            share|cite|improve this answer




























                              5














                              Let $f : mathbb{R} to mathbb{R}$ be given by $f(x)=a^x$ and consider the $ln$ function. We can take the composition so that we have:



                              $$(lncirc f)(x)=ln (a^x)=xln a$$



                              Now, if we take the derivative, on the left hand side we use the chain rule and on the right hand side we differentiate as usual so that we have:



                              $$frac{f'(x)}{f(x)}=ln a$$



                              Now solving for $f'(x)$ gives $f'(x) = f(x) ln a$ so that $f'(x) = a^x ln a$. This useful technique can be used to take derivatives of other functions: we compose the original function with the inverse and then differentiate on both sides and use the same idea we've used here, this technique can simplify many derivatives and save a lot of time in some situations.






                              share|cite|improve this answer


























                                5












                                5








                                5






                                Let $f : mathbb{R} to mathbb{R}$ be given by $f(x)=a^x$ and consider the $ln$ function. We can take the composition so that we have:



                                $$(lncirc f)(x)=ln (a^x)=xln a$$



                                Now, if we take the derivative, on the left hand side we use the chain rule and on the right hand side we differentiate as usual so that we have:



                                $$frac{f'(x)}{f(x)}=ln a$$



                                Now solving for $f'(x)$ gives $f'(x) = f(x) ln a$ so that $f'(x) = a^x ln a$. This useful technique can be used to take derivatives of other functions: we compose the original function with the inverse and then differentiate on both sides and use the same idea we've used here, this technique can simplify many derivatives and save a lot of time in some situations.






                                share|cite|improve this answer














                                Let $f : mathbb{R} to mathbb{R}$ be given by $f(x)=a^x$ and consider the $ln$ function. We can take the composition so that we have:



                                $$(lncirc f)(x)=ln (a^x)=xln a$$



                                Now, if we take the derivative, on the left hand side we use the chain rule and on the right hand side we differentiate as usual so that we have:



                                $$frac{f'(x)}{f(x)}=ln a$$



                                Now solving for $f'(x)$ gives $f'(x) = f(x) ln a$ so that $f'(x) = a^x ln a$. This useful technique can be used to take derivatives of other functions: we compose the original function with the inverse and then differentiate on both sides and use the same idea we've used here, this technique can simplify many derivatives and save a lot of time in some situations.







                                share|cite|improve this answer














                                share|cite|improve this answer



                                share|cite|improve this answer








                                edited Jan 5 '15 at 23:28

























                                answered May 22 '13 at 3:58









                                user1620696

                                11.5k341114




                                11.5k341114























                                    3














                                    Hint: Write $y = a^x$ or equivalently $ln y = x ln a$ and use implicit differentiation.






                                    share|cite|improve this answer


























                                      3














                                      Hint: Write $y = a^x$ or equivalently $ln y = x ln a$ and use implicit differentiation.






                                      share|cite|improve this answer
























                                        3












                                        3








                                        3






                                        Hint: Write $y = a^x$ or equivalently $ln y = x ln a$ and use implicit differentiation.






                                        share|cite|improve this answer












                                        Hint: Write $y = a^x$ or equivalently $ln y = x ln a$ and use implicit differentiation.







                                        share|cite|improve this answer












                                        share|cite|improve this answer



                                        share|cite|improve this answer










                                        answered May 22 '13 at 3:28









                                        response

                                        4,70121220




                                        4,70121220























                                            1














                                            enter image description here, the last term, enter image description here, can be explained by L'Hopital's rule, just taking the limits of the numerator and denominator one of each time.






                                            share|cite|improve this answer


























                                              1














                                              enter image description here, the last term, enter image description here, can be explained by L'Hopital's rule, just taking the limits of the numerator and denominator one of each time.






                                              share|cite|improve this answer
























                                                1












                                                1








                                                1






                                                enter image description here, the last term, enter image description here, can be explained by L'Hopital's rule, just taking the limits of the numerator and denominator one of each time.






                                                share|cite|improve this answer












                                                enter image description here, the last term, enter image description here, can be explained by L'Hopital's rule, just taking the limits of the numerator and denominator one of each time.







                                                share|cite|improve this answer












                                                share|cite|improve this answer



                                                share|cite|improve this answer










                                                answered Feb 24 '14 at 0:22









                                                user131054

                                                111




                                                111























                                                    0














                                                    Here are the steps
                                                    $$
                                                    frac{d}{dx} left[a^xright] = frac{d}{dx} left[e^{ln a^x}right]= e^{ln a^x} frac{d}{dx} left[ln a^xright]
                                                    $$
                                                    $$
                                                    = a^x frac{d}{dx} left[xln aright] = a^xleft(ln aright)frac{d}{dx} left[xright]= a^xln a
                                                    $$






                                                    share|cite|improve this answer


























                                                      0














                                                      Here are the steps
                                                      $$
                                                      frac{d}{dx} left[a^xright] = frac{d}{dx} left[e^{ln a^x}right]= e^{ln a^x} frac{d}{dx} left[ln a^xright]
                                                      $$
                                                      $$
                                                      = a^x frac{d}{dx} left[xln aright] = a^xleft(ln aright)frac{d}{dx} left[xright]= a^xln a
                                                      $$






                                                      share|cite|improve this answer
























                                                        0












                                                        0








                                                        0






                                                        Here are the steps
                                                        $$
                                                        frac{d}{dx} left[a^xright] = frac{d}{dx} left[e^{ln a^x}right]= e^{ln a^x} frac{d}{dx} left[ln a^xright]
                                                        $$
                                                        $$
                                                        = a^x frac{d}{dx} left[xln aright] = a^xleft(ln aright)frac{d}{dx} left[xright]= a^xln a
                                                        $$






                                                        share|cite|improve this answer












                                                        Here are the steps
                                                        $$
                                                        frac{d}{dx} left[a^xright] = frac{d}{dx} left[e^{ln a^x}right]= e^{ln a^x} frac{d}{dx} left[ln a^xright]
                                                        $$
                                                        $$
                                                        = a^x frac{d}{dx} left[xln aright] = a^xleft(ln aright)frac{d}{dx} left[xright]= a^xln a
                                                        $$







                                                        share|cite|improve this answer












                                                        share|cite|improve this answer



                                                        share|cite|improve this answer










                                                        answered Jan 5 '15 at 18:06









                                                        k170

                                                        7,45131540




                                                        7,45131540























                                                            0














                                                            $ frac{d}{dx} a^x=$



                                                            $=d/dx$ $e^{ln (a^x)}=$



                                                            $=d/dx e^{xln(a)}$ just as you said.



                                                            Now it's time for chain rule.



                                                            $f(x)=e^x$



                                                            $g(x)=x*ln(a)$



                                                            $a^x= f(g(x))$



                                                            last comment before I get solving



                                                            $a=e^{ln(a)}$



                                                            now let's get it done



                                                            $d/dx e^{x ln(a)}=$



                                                            $=e^{x*ln(a)} d/dx (x ln(a))=$ (by chain rule)



                                                            $=e^{x ln(a)} * ln(a)$



                                                            and that is the solution. Wait it doesnt look correct --> we should do some algebra!



                                                            Show for yourself that



                                                            $e^{x*ln(a)}=( e^{ln(a)} )^x$ but as we said that $a = e^{ln(a)}$ so $( e^{ln(a)} )^x$ actually equals $a^x$ and of course $e^{x*ln(a)}$ equals a^x



                                                            With what we just said you can see that $e^{x * ln(a)} ln(a)$ equals $a^x ln(a)$ or



                                                            $$d/dx a^x = a^x ln(a)$$






                                                            share|cite|improve this answer



















                                                            • 1




                                                              Use TeX while typing math symbols
                                                              – supremum
                                                              Jan 5 '15 at 17:59










                                                            • For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                              – Ruslan
                                                              Jan 5 '15 at 18:43


















                                                            0














                                                            $ frac{d}{dx} a^x=$



                                                            $=d/dx$ $e^{ln (a^x)}=$



                                                            $=d/dx e^{xln(a)}$ just as you said.



                                                            Now it's time for chain rule.



                                                            $f(x)=e^x$



                                                            $g(x)=x*ln(a)$



                                                            $a^x= f(g(x))$



                                                            last comment before I get solving



                                                            $a=e^{ln(a)}$



                                                            now let's get it done



                                                            $d/dx e^{x ln(a)}=$



                                                            $=e^{x*ln(a)} d/dx (x ln(a))=$ (by chain rule)



                                                            $=e^{x ln(a)} * ln(a)$



                                                            and that is the solution. Wait it doesnt look correct --> we should do some algebra!



                                                            Show for yourself that



                                                            $e^{x*ln(a)}=( e^{ln(a)} )^x$ but as we said that $a = e^{ln(a)}$ so $( e^{ln(a)} )^x$ actually equals $a^x$ and of course $e^{x*ln(a)}$ equals a^x



                                                            With what we just said you can see that $e^{x * ln(a)} ln(a)$ equals $a^x ln(a)$ or



                                                            $$d/dx a^x = a^x ln(a)$$






                                                            share|cite|improve this answer



















                                                            • 1




                                                              Use TeX while typing math symbols
                                                              – supremum
                                                              Jan 5 '15 at 17:59










                                                            • For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                              – Ruslan
                                                              Jan 5 '15 at 18:43
















                                                            0












                                                            0








                                                            0






                                                            $ frac{d}{dx} a^x=$



                                                            $=d/dx$ $e^{ln (a^x)}=$



                                                            $=d/dx e^{xln(a)}$ just as you said.



                                                            Now it's time for chain rule.



                                                            $f(x)=e^x$



                                                            $g(x)=x*ln(a)$



                                                            $a^x= f(g(x))$



                                                            last comment before I get solving



                                                            $a=e^{ln(a)}$



                                                            now let's get it done



                                                            $d/dx e^{x ln(a)}=$



                                                            $=e^{x*ln(a)} d/dx (x ln(a))=$ (by chain rule)



                                                            $=e^{x ln(a)} * ln(a)$



                                                            and that is the solution. Wait it doesnt look correct --> we should do some algebra!



                                                            Show for yourself that



                                                            $e^{x*ln(a)}=( e^{ln(a)} )^x$ but as we said that $a = e^{ln(a)}$ so $( e^{ln(a)} )^x$ actually equals $a^x$ and of course $e^{x*ln(a)}$ equals a^x



                                                            With what we just said you can see that $e^{x * ln(a)} ln(a)$ equals $a^x ln(a)$ or



                                                            $$d/dx a^x = a^x ln(a)$$






                                                            share|cite|improve this answer














                                                            $ frac{d}{dx} a^x=$



                                                            $=d/dx$ $e^{ln (a^x)}=$



                                                            $=d/dx e^{xln(a)}$ just as you said.



                                                            Now it's time for chain rule.



                                                            $f(x)=e^x$



                                                            $g(x)=x*ln(a)$



                                                            $a^x= f(g(x))$



                                                            last comment before I get solving



                                                            $a=e^{ln(a)}$



                                                            now let's get it done



                                                            $d/dx e^{x ln(a)}=$



                                                            $=e^{x*ln(a)} d/dx (x ln(a))=$ (by chain rule)



                                                            $=e^{x ln(a)} * ln(a)$



                                                            and that is the solution. Wait it doesnt look correct --> we should do some algebra!



                                                            Show for yourself that



                                                            $e^{x*ln(a)}=( e^{ln(a)} )^x$ but as we said that $a = e^{ln(a)}$ so $( e^{ln(a)} )^x$ actually equals $a^x$ and of course $e^{x*ln(a)}$ equals a^x



                                                            With what we just said you can see that $e^{x * ln(a)} ln(a)$ equals $a^x ln(a)$ or



                                                            $$d/dx a^x = a^x ln(a)$$







                                                            share|cite|improve this answer














                                                            share|cite|improve this answer



                                                            share|cite|improve this answer








                                                            edited Jan 9 '15 at 20:35









                                                            Community

                                                            1




                                                            1










                                                            answered Jan 5 '15 at 17:29









                                                            grekiki

                                                            1




                                                            1








                                                            • 1




                                                              Use TeX while typing math symbols
                                                              – supremum
                                                              Jan 5 '15 at 17:59










                                                            • For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                              – Ruslan
                                                              Jan 5 '15 at 18:43
















                                                            • 1




                                                              Use TeX while typing math symbols
                                                              – supremum
                                                              Jan 5 '15 at 17:59










                                                            • For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                              – Ruslan
                                                              Jan 5 '15 at 18:43










                                                            1




                                                            1




                                                            Use TeX while typing math symbols
                                                            – supremum
                                                            Jan 5 '15 at 17:59




                                                            Use TeX while typing math symbols
                                                            – supremum
                                                            Jan 5 '15 at 17:59












                                                            For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                            – Ruslan
                                                            Jan 5 '15 at 18:43






                                                            For help, see this FAQ entry about $LaTeX$ on Math.SE.
                                                            – Ruslan
                                                            Jan 5 '15 at 18:43













                                                            -1














                                                            Let $y = a^x$



                                                            Then taking log on both side to the base $e$



                                                            We have;



                                                            $ ln y = ln a^x$



                                                            $ ln y = xcdot ln a$



                                                            Taking derivative with respect to $x$;



                                                            $frac d{dx} ln y = frac d{dx} xcdot ln a$



                                                            (I have applied chain rule here>>)



                                                            $ frac 1y frac{dy}{dx} = ln a + 0$



                                                            $ frac {dy}{dx} = ycdot ln a$



                                                            We know $y= a^x$



                                                            So, $frac {dy}{dx} = a^x ln a$



                                                            Hope it was easier than other methodologies used to derive it!






                                                            share|cite|improve this answer























                                                            • The question is five years old and your answer adds nothing new to the already existing answers.
                                                              – José Carlos Santos
                                                              Nov 21 '18 at 9:39
















                                                            -1














                                                            Let $y = a^x$



                                                            Then taking log on both side to the base $e$



                                                            We have;



                                                            $ ln y = ln a^x$



                                                            $ ln y = xcdot ln a$



                                                            Taking derivative with respect to $x$;



                                                            $frac d{dx} ln y = frac d{dx} xcdot ln a$



                                                            (I have applied chain rule here>>)



                                                            $ frac 1y frac{dy}{dx} = ln a + 0$



                                                            $ frac {dy}{dx} = ycdot ln a$



                                                            We know $y= a^x$



                                                            So, $frac {dy}{dx} = a^x ln a$



                                                            Hope it was easier than other methodologies used to derive it!






                                                            share|cite|improve this answer























                                                            • The question is five years old and your answer adds nothing new to the already existing answers.
                                                              – José Carlos Santos
                                                              Nov 21 '18 at 9:39














                                                            -1












                                                            -1








                                                            -1






                                                            Let $y = a^x$



                                                            Then taking log on both side to the base $e$



                                                            We have;



                                                            $ ln y = ln a^x$



                                                            $ ln y = xcdot ln a$



                                                            Taking derivative with respect to $x$;



                                                            $frac d{dx} ln y = frac d{dx} xcdot ln a$



                                                            (I have applied chain rule here>>)



                                                            $ frac 1y frac{dy}{dx} = ln a + 0$



                                                            $ frac {dy}{dx} = ycdot ln a$



                                                            We know $y= a^x$



                                                            So, $frac {dy}{dx} = a^x ln a$



                                                            Hope it was easier than other methodologies used to derive it!






                                                            share|cite|improve this answer














                                                            Let $y = a^x$



                                                            Then taking log on both side to the base $e$



                                                            We have;



                                                            $ ln y = ln a^x$



                                                            $ ln y = xcdot ln a$



                                                            Taking derivative with respect to $x$;



                                                            $frac d{dx} ln y = frac d{dx} xcdot ln a$



                                                            (I have applied chain rule here>>)



                                                            $ frac 1y frac{dy}{dx} = ln a + 0$



                                                            $ frac {dy}{dx} = ycdot ln a$



                                                            We know $y= a^x$



                                                            So, $frac {dy}{dx} = a^x ln a$



                                                            Hope it was easier than other methodologies used to derive it!







                                                            share|cite|improve this answer














                                                            share|cite|improve this answer



                                                            share|cite|improve this answer








                                                            edited Nov 21 '18 at 9:46









                                                            idea

                                                            2,15441025




                                                            2,15441025










                                                            answered Nov 21 '18 at 9:17









                                                            Vichitra Attri

                                                            11




                                                            11












                                                            • The question is five years old and your answer adds nothing new to the already existing answers.
                                                              – José Carlos Santos
                                                              Nov 21 '18 at 9:39


















                                                            • The question is five years old and your answer adds nothing new to the already existing answers.
                                                              – José Carlos Santos
                                                              Nov 21 '18 at 9:39
















                                                            The question is five years old and your answer adds nothing new to the already existing answers.
                                                            – José Carlos Santos
                                                            Nov 21 '18 at 9:39




                                                            The question is five years old and your answer adds nothing new to the already existing answers.
                                                            – José Carlos Santos
                                                            Nov 21 '18 at 9:39


















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