Prove or disprove the inequality $ -xln (x)leq ln(1-x)(ln (x) + 1 - x)$












2












$begingroup$


how can one disprove or prove the equation below? I have already reduced it to its simplest form (according to me) and I am kind of stuck at this point:



$$ -xln (x)leq ln(1-x)(ln (x) + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



Any help will be quite useful to me. Thanks.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    prove/disprove, not "approve/disapprove"
    $endgroup$
    – rschwieb
    Jan 11 at 17:49










  • $begingroup$
    Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:52










  • $begingroup$
    @Dr.SonnhardGraubner yes I mean that
    $endgroup$
    – Weez Khan
    Jan 11 at 17:53












  • $begingroup$
    I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
    $endgroup$
    – 6005
    Jan 11 at 17:55










  • $begingroup$
    This inequalitiy is not true, take $$x=frac{1}{2}$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:56
















2












$begingroup$


how can one disprove or prove the equation below? I have already reduced it to its simplest form (according to me) and I am kind of stuck at this point:



$$ -xln (x)leq ln(1-x)(ln (x) + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



Any help will be quite useful to me. Thanks.










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    prove/disprove, not "approve/disapprove"
    $endgroup$
    – rschwieb
    Jan 11 at 17:49










  • $begingroup$
    Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:52










  • $begingroup$
    @Dr.SonnhardGraubner yes I mean that
    $endgroup$
    – Weez Khan
    Jan 11 at 17:53












  • $begingroup$
    I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
    $endgroup$
    – 6005
    Jan 11 at 17:55










  • $begingroup$
    This inequalitiy is not true, take $$x=frac{1}{2}$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:56














2












2








2





$begingroup$


how can one disprove or prove the equation below? I have already reduced it to its simplest form (according to me) and I am kind of stuck at this point:



$$ -xln (x)leq ln(1-x)(ln (x) + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



Any help will be quite useful to me. Thanks.










share|cite|improve this question











$endgroup$




how can one disprove or prove the equation below? I have already reduced it to its simplest form (according to me) and I am kind of stuck at this point:



$$ -xln (x)leq ln(1-x)(ln (x) + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



Any help will be quite useful to me. Thanks.







inequality logarithms






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 11 at 18:06









6005

36.2k751125




36.2k751125










asked Jan 11 at 17:46









Weez KhanWeez Khan

135




135








  • 1




    $begingroup$
    prove/disprove, not "approve/disapprove"
    $endgroup$
    – rschwieb
    Jan 11 at 17:49










  • $begingroup$
    Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:52










  • $begingroup$
    @Dr.SonnhardGraubner yes I mean that
    $endgroup$
    – Weez Khan
    Jan 11 at 17:53












  • $begingroup$
    I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
    $endgroup$
    – 6005
    Jan 11 at 17:55










  • $begingroup$
    This inequalitiy is not true, take $$x=frac{1}{2}$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:56














  • 1




    $begingroup$
    prove/disprove, not "approve/disapprove"
    $endgroup$
    – rschwieb
    Jan 11 at 17:49










  • $begingroup$
    Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:52










  • $begingroup$
    @Dr.SonnhardGraubner yes I mean that
    $endgroup$
    – Weez Khan
    Jan 11 at 17:53












  • $begingroup$
    I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
    $endgroup$
    – 6005
    Jan 11 at 17:55










  • $begingroup$
    This inequalitiy is not true, take $$x=frac{1}{2}$$
    $endgroup$
    – Dr. Sonnhard Graubner
    Jan 11 at 17:56








1




1




$begingroup$
prove/disprove, not "approve/disapprove"
$endgroup$
– rschwieb
Jan 11 at 17:49




$begingroup$
prove/disprove, not "approve/disapprove"
$endgroup$
– rschwieb
Jan 11 at 17:49












$begingroup$
Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
$endgroup$
– Dr. Sonnhard Graubner
Jan 11 at 17:52




$begingroup$
Do you mean $$-xln(x)le ln(1-x)(ln(x)+1-x)$$
$endgroup$
– Dr. Sonnhard Graubner
Jan 11 at 17:52












$begingroup$
@Dr.SonnhardGraubner yes I mean that
$endgroup$
– Weez Khan
Jan 11 at 17:53






$begingroup$
@Dr.SonnhardGraubner yes I mean that
$endgroup$
– Weez Khan
Jan 11 at 17:53














$begingroup$
I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
$endgroup$
– 6005
Jan 11 at 17:55




$begingroup$
I think you mean $ge$, not $le$. The inequality you wrote down is not true for $0 < x < 1$, but if you switch it to $ge$ instead of $le$ then it is true.
$endgroup$
– 6005
Jan 11 at 17:55












$begingroup$
This inequalitiy is not true, take $$x=frac{1}{2}$$
$endgroup$
– Dr. Sonnhard Graubner
Jan 11 at 17:56




$begingroup$
This inequalitiy is not true, take $$x=frac{1}{2}$$
$endgroup$
– Dr. Sonnhard Graubner
Jan 11 at 17:56










4 Answers
4






active

oldest

votes


















0












$begingroup$

The inequality
$$ -xln xleq ln(1-x)(ln x + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



is not true.
For example, if we put in $x = frac{1}{2}$ we get
$$
- frac{1}{2} ln frac{1}{2} = frac12 ln 2 = 0.34ldots
$$

and
$$
lnleft(1 - frac12right)
left( ln frac12 + 1 - frac12right)
= left(- ln 2 right) left( frac12 - ln 2 right) = (ln 2)^2 - frac12 ln 2 = 0.13 ldots
$$



and $0.34 ldots > 0.13ldots$.





You probably made a mistake when you reduced it to this form. If you reverse the inequality, it would be true.
See the graph below:



enter image description here



We can see that the graph looks to be $> 0$ for $0 < x < 1$.
So we conjecture that the inequality
$$
- x ln x ge ln(1-x) (ln x + 1 - x)
$$

will be true.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
    $endgroup$
    – Weez Khan
    Jan 11 at 18:06



















0












$begingroup$

Hint: We have $$-ln(1-x)(ln(x)+1-x)-xln(x)geq 0$$ for $$0<x<1$$






share|cite|improve this answer









$endgroup$





















    0












    $begingroup$

    Define
    begin{align*}
    f(x) = -xlog(x) - log(1-x)(log(x) + 1 - x)
    end{align*}

    It suffices to prove $f(x) ge 0$ for $x in [0, 1]$. Note that
    begin{align*}
    f(0) &= f(1) = 0 \
    f'(x) &= frac{(x-1)log(1-x)}{x} + frac{xlog(x)}{1-x} begin{cases}
    > 0 & x < frac{1}{2} \
    = 0 & x = frac{1}{2} \
    < 0 & x > frac{1}{2}
    end{cases}
    end{align*}

    Therefore, $f(x) ge min(f(0), f(1)) = 0$ for $x in [0, 1]$, as desired.






    share|cite|improve this answer









    $endgroup$





















      0












      $begingroup$

      Consider the function
      $$f(x)=xln (x)+ ln(1-x),(ln (x) + 1 - x) $$ and notice the symmetry which makes that
      $$f(x)+f(1-x)=0$$ Compute $f(x)$ anywhere to show that is negative. Using $x=frac 12$, you have $(log (2)-1) log (2)$ which is the minimum value.






      share|cite|improve this answer









      $endgroup$













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        4 Answers
        4






        active

        oldest

        votes








        4 Answers
        4






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        0












        $begingroup$

        The inequality
        $$ -xln xleq ln(1-x)(ln x + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



        is not true.
        For example, if we put in $x = frac{1}{2}$ we get
        $$
        - frac{1}{2} ln frac{1}{2} = frac12 ln 2 = 0.34ldots
        $$

        and
        $$
        lnleft(1 - frac12right)
        left( ln frac12 + 1 - frac12right)
        = left(- ln 2 right) left( frac12 - ln 2 right) = (ln 2)^2 - frac12 ln 2 = 0.13 ldots
        $$



        and $0.34 ldots > 0.13ldots$.





        You probably made a mistake when you reduced it to this form. If you reverse the inequality, it would be true.
        See the graph below:



        enter image description here



        We can see that the graph looks to be $> 0$ for $0 < x < 1$.
        So we conjecture that the inequality
        $$
        - x ln x ge ln(1-x) (ln x + 1 - x)
        $$

        will be true.






        share|cite|improve this answer









        $endgroup$













        • $begingroup$
          Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
          $endgroup$
          – Weez Khan
          Jan 11 at 18:06
















        0












        $begingroup$

        The inequality
        $$ -xln xleq ln(1-x)(ln x + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



        is not true.
        For example, if we put in $x = frac{1}{2}$ we get
        $$
        - frac{1}{2} ln frac{1}{2} = frac12 ln 2 = 0.34ldots
        $$

        and
        $$
        lnleft(1 - frac12right)
        left( ln frac12 + 1 - frac12right)
        = left(- ln 2 right) left( frac12 - ln 2 right) = (ln 2)^2 - frac12 ln 2 = 0.13 ldots
        $$



        and $0.34 ldots > 0.13ldots$.





        You probably made a mistake when you reduced it to this form. If you reverse the inequality, it would be true.
        See the graph below:



        enter image description here



        We can see that the graph looks to be $> 0$ for $0 < x < 1$.
        So we conjecture that the inequality
        $$
        - x ln x ge ln(1-x) (ln x + 1 - x)
        $$

        will be true.






        share|cite|improve this answer









        $endgroup$













        • $begingroup$
          Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
          $endgroup$
          – Weez Khan
          Jan 11 at 18:06














        0












        0








        0





        $begingroup$

        The inequality
        $$ -xln xleq ln(1-x)(ln x + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



        is not true.
        For example, if we put in $x = frac{1}{2}$ we get
        $$
        - frac{1}{2} ln frac{1}{2} = frac12 ln 2 = 0.34ldots
        $$

        and
        $$
        lnleft(1 - frac12right)
        left( ln frac12 + 1 - frac12right)
        = left(- ln 2 right) left( frac12 - ln 2 right) = (ln 2)^2 - frac12 ln 2 = 0.13 ldots
        $$



        and $0.34 ldots > 0.13ldots$.





        You probably made a mistake when you reduced it to this form. If you reverse the inequality, it would be true.
        See the graph below:



        enter image description here



        We can see that the graph looks to be $> 0$ for $0 < x < 1$.
        So we conjecture that the inequality
        $$
        - x ln x ge ln(1-x) (ln x + 1 - x)
        $$

        will be true.






        share|cite|improve this answer









        $endgroup$



        The inequality
        $$ -xln xleq ln(1-x)(ln x + 1 - x) qquadtext{for}qquad 0lt xlt 1$$



        is not true.
        For example, if we put in $x = frac{1}{2}$ we get
        $$
        - frac{1}{2} ln frac{1}{2} = frac12 ln 2 = 0.34ldots
        $$

        and
        $$
        lnleft(1 - frac12right)
        left( ln frac12 + 1 - frac12right)
        = left(- ln 2 right) left( frac12 - ln 2 right) = (ln 2)^2 - frac12 ln 2 = 0.13 ldots
        $$



        and $0.34 ldots > 0.13ldots$.





        You probably made a mistake when you reduced it to this form. If you reverse the inequality, it would be true.
        See the graph below:



        enter image description here



        We can see that the graph looks to be $> 0$ for $0 < x < 1$.
        So we conjecture that the inequality
        $$
        - x ln x ge ln(1-x) (ln x + 1 - x)
        $$

        will be true.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 11 at 18:04









        60056005

        36.2k751125




        36.2k751125












        • $begingroup$
          Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
          $endgroup$
          – Weez Khan
          Jan 11 at 18:06


















        • $begingroup$
          Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
          $endgroup$
          – Weez Khan
          Jan 11 at 18:06
















        $begingroup$
        Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
        $endgroup$
        – Weez Khan
        Jan 11 at 18:06




        $begingroup$
        Thank you, just one more question, can we reduce the equation further(make it more simpler) so that it is intuitively possible as to why it is not possible
        $endgroup$
        – Weez Khan
        Jan 11 at 18:06











        0












        $begingroup$

        Hint: We have $$-ln(1-x)(ln(x)+1-x)-xln(x)geq 0$$ for $$0<x<1$$






        share|cite|improve this answer









        $endgroup$


















          0












          $begingroup$

          Hint: We have $$-ln(1-x)(ln(x)+1-x)-xln(x)geq 0$$ for $$0<x<1$$






          share|cite|improve this answer









          $endgroup$
















            0












            0








            0





            $begingroup$

            Hint: We have $$-ln(1-x)(ln(x)+1-x)-xln(x)geq 0$$ for $$0<x<1$$






            share|cite|improve this answer









            $endgroup$



            Hint: We have $$-ln(1-x)(ln(x)+1-x)-xln(x)geq 0$$ for $$0<x<1$$







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Jan 11 at 18:08









            Dr. Sonnhard GraubnerDr. Sonnhard Graubner

            75.1k42865




            75.1k42865























                0












                $begingroup$

                Define
                begin{align*}
                f(x) = -xlog(x) - log(1-x)(log(x) + 1 - x)
                end{align*}

                It suffices to prove $f(x) ge 0$ for $x in [0, 1]$. Note that
                begin{align*}
                f(0) &= f(1) = 0 \
                f'(x) &= frac{(x-1)log(1-x)}{x} + frac{xlog(x)}{1-x} begin{cases}
                > 0 & x < frac{1}{2} \
                = 0 & x = frac{1}{2} \
                < 0 & x > frac{1}{2}
                end{cases}
                end{align*}

                Therefore, $f(x) ge min(f(0), f(1)) = 0$ for $x in [0, 1]$, as desired.






                share|cite|improve this answer









                $endgroup$


















                  0












                  $begingroup$

                  Define
                  begin{align*}
                  f(x) = -xlog(x) - log(1-x)(log(x) + 1 - x)
                  end{align*}

                  It suffices to prove $f(x) ge 0$ for $x in [0, 1]$. Note that
                  begin{align*}
                  f(0) &= f(1) = 0 \
                  f'(x) &= frac{(x-1)log(1-x)}{x} + frac{xlog(x)}{1-x} begin{cases}
                  > 0 & x < frac{1}{2} \
                  = 0 & x = frac{1}{2} \
                  < 0 & x > frac{1}{2}
                  end{cases}
                  end{align*}

                  Therefore, $f(x) ge min(f(0), f(1)) = 0$ for $x in [0, 1]$, as desired.






                  share|cite|improve this answer









                  $endgroup$
















                    0












                    0








                    0





                    $begingroup$

                    Define
                    begin{align*}
                    f(x) = -xlog(x) - log(1-x)(log(x) + 1 - x)
                    end{align*}

                    It suffices to prove $f(x) ge 0$ for $x in [0, 1]$. Note that
                    begin{align*}
                    f(0) &= f(1) = 0 \
                    f'(x) &= frac{(x-1)log(1-x)}{x} + frac{xlog(x)}{1-x} begin{cases}
                    > 0 & x < frac{1}{2} \
                    = 0 & x = frac{1}{2} \
                    < 0 & x > frac{1}{2}
                    end{cases}
                    end{align*}

                    Therefore, $f(x) ge min(f(0), f(1)) = 0$ for $x in [0, 1]$, as desired.






                    share|cite|improve this answer









                    $endgroup$



                    Define
                    begin{align*}
                    f(x) = -xlog(x) - log(1-x)(log(x) + 1 - x)
                    end{align*}

                    It suffices to prove $f(x) ge 0$ for $x in [0, 1]$. Note that
                    begin{align*}
                    f(0) &= f(1) = 0 \
                    f'(x) &= frac{(x-1)log(1-x)}{x} + frac{xlog(x)}{1-x} begin{cases}
                    > 0 & x < frac{1}{2} \
                    = 0 & x = frac{1}{2} \
                    < 0 & x > frac{1}{2}
                    end{cases}
                    end{align*}

                    Therefore, $f(x) ge min(f(0), f(1)) = 0$ for $x in [0, 1]$, as desired.







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered Jan 11 at 18:36









                    Tom ChenTom Chen

                    913513




                    913513























                        0












                        $begingroup$

                        Consider the function
                        $$f(x)=xln (x)+ ln(1-x),(ln (x) + 1 - x) $$ and notice the symmetry which makes that
                        $$f(x)+f(1-x)=0$$ Compute $f(x)$ anywhere to show that is negative. Using $x=frac 12$, you have $(log (2)-1) log (2)$ which is the minimum value.






                        share|cite|improve this answer









                        $endgroup$


















                          0












                          $begingroup$

                          Consider the function
                          $$f(x)=xln (x)+ ln(1-x),(ln (x) + 1 - x) $$ and notice the symmetry which makes that
                          $$f(x)+f(1-x)=0$$ Compute $f(x)$ anywhere to show that is negative. Using $x=frac 12$, you have $(log (2)-1) log (2)$ which is the minimum value.






                          share|cite|improve this answer









                          $endgroup$
















                            0












                            0








                            0





                            $begingroup$

                            Consider the function
                            $$f(x)=xln (x)+ ln(1-x),(ln (x) + 1 - x) $$ and notice the symmetry which makes that
                            $$f(x)+f(1-x)=0$$ Compute $f(x)$ anywhere to show that is negative. Using $x=frac 12$, you have $(log (2)-1) log (2)$ which is the minimum value.






                            share|cite|improve this answer









                            $endgroup$



                            Consider the function
                            $$f(x)=xln (x)+ ln(1-x),(ln (x) + 1 - x) $$ and notice the symmetry which makes that
                            $$f(x)+f(1-x)=0$$ Compute $f(x)$ anywhere to show that is negative. Using $x=frac 12$, you have $(log (2)-1) log (2)$ which is the minimum value.







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered Jan 12 at 7:04









                            Claude LeiboviciClaude Leibovici

                            121k1157133




                            121k1157133






























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