Is a function less than a decreasing function also decreasing?












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Two families of functions, $f_alpha(x)$ and $g_alpha(x)$, where $0leqalpha, xleq 1$.



It is known that $f_alpha(0)=g_alpha(0)=1$ and $f_alpha(1)=g_alpha(1)=0$ for any $alpha$.



Also, $f_0(x)=g_0(x)leq 1$ and $f_1(x)=g_1(x)=1$ for any $xin[0, 1]$.



Knowing that $g_alpha(x)$ decreases in $x$ for any $alpha$, can we say the same for $f_alpha$?










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  • 2




    $begingroup$
    Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
    $endgroup$
    – jonem
    Jan 12 at 20:03
















1












$begingroup$


Two families of functions, $f_alpha(x)$ and $g_alpha(x)$, where $0leqalpha, xleq 1$.



It is known that $f_alpha(0)=g_alpha(0)=1$ and $f_alpha(1)=g_alpha(1)=0$ for any $alpha$.



Also, $f_0(x)=g_0(x)leq 1$ and $f_1(x)=g_1(x)=1$ for any $xin[0, 1]$.



Knowing that $g_alpha(x)$ decreases in $x$ for any $alpha$, can we say the same for $f_alpha$?










share|cite|improve this question











$endgroup$








  • 2




    $begingroup$
    Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
    $endgroup$
    – jonem
    Jan 12 at 20:03














1












1








1





$begingroup$


Two families of functions, $f_alpha(x)$ and $g_alpha(x)$, where $0leqalpha, xleq 1$.



It is known that $f_alpha(0)=g_alpha(0)=1$ and $f_alpha(1)=g_alpha(1)=0$ for any $alpha$.



Also, $f_0(x)=g_0(x)leq 1$ and $f_1(x)=g_1(x)=1$ for any $xin[0, 1]$.



Knowing that $g_alpha(x)$ decreases in $x$ for any $alpha$, can we say the same for $f_alpha$?










share|cite|improve this question











$endgroup$




Two families of functions, $f_alpha(x)$ and $g_alpha(x)$, where $0leqalpha, xleq 1$.



It is known that $f_alpha(0)=g_alpha(0)=1$ and $f_alpha(1)=g_alpha(1)=0$ for any $alpha$.



Also, $f_0(x)=g_0(x)leq 1$ and $f_1(x)=g_1(x)=1$ for any $xin[0, 1]$.



Knowing that $g_alpha(x)$ decreases in $x$ for any $alpha$, can we say the same for $f_alpha$?







real-analysis calculus functions






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edited Jan 13 at 15:06









daw

24.3k1645




24.3k1645










asked Jan 12 at 20:00









HHWWHHWW

62




62








  • 2




    $begingroup$
    Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
    $endgroup$
    – jonem
    Jan 12 at 20:03














  • 2




    $begingroup$
    Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
    $endgroup$
    – jonem
    Jan 12 at 20:03








2




2




$begingroup$
Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
$endgroup$
– jonem
Jan 12 at 20:03




$begingroup$
Try drawing this out; you should be able to come up with an example where $f$ decreases at a faster rate in one region, then increases for a bit, then decreases again, all while being below $g$.
$endgroup$
– jonem
Jan 12 at 20:03










1 Answer
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$begingroup$

Here we have $fle g$ and $g$ is decreasing but, as you can see from the picture, nothing can be deduced regarding if $f$ is increasing or decreasing.



enter image description here






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    4












    $begingroup$

    Here we have $fle g$ and $g$ is decreasing but, as you can see from the picture, nothing can be deduced regarding if $f$ is increasing or decreasing.



    enter image description here






    share|cite|improve this answer









    $endgroup$


















      4












      $begingroup$

      Here we have $fle g$ and $g$ is decreasing but, as you can see from the picture, nothing can be deduced regarding if $f$ is increasing or decreasing.



      enter image description here






      share|cite|improve this answer









      $endgroup$
















        4












        4








        4





        $begingroup$

        Here we have $fle g$ and $g$ is decreasing but, as you can see from the picture, nothing can be deduced regarding if $f$ is increasing or decreasing.



        enter image description here






        share|cite|improve this answer









        $endgroup$



        Here we have $fle g$ and $g$ is decreasing but, as you can see from the picture, nothing can be deduced regarding if $f$ is increasing or decreasing.



        enter image description here







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 12 at 20:13









        BigbearZzzBigbearZzz

        8,69121652




        8,69121652






























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