There is c such that $f''(c)g(c)+f(c)g''(c)+f'(c)g'(c)=0$












0












$begingroup$


Let $f,g:[a,b]tomathbb{R}$ both increasing, twice differentiable and $g$ is also convex, $f(a)=0$, $g(b)=0$, $f^prime(a)=0$. Prove that there exists $cin(a,b)$ such that
$$f''(c)g(c)+f(c)g''(c)+f'(c)g'(c)=0$$



I found that if we denote by $h(x)=f''(x)g(x)+f(x)g''(x)+f'(x)g'(x)$, we have that $h$ has the intermediate value property and, also, $h(a)leq 0$ and $h(b)>0$. I'm stuck only if $h(a)=0$.










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$endgroup$












  • $begingroup$
    Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
    $endgroup$
    – GReyes
    Jan 17 at 22:40










  • $begingroup$
    I'm afraid I am
    $endgroup$
    – Andrew V
    Jan 17 at 23:25
















0












$begingroup$


Let $f,g:[a,b]tomathbb{R}$ both increasing, twice differentiable and $g$ is also convex, $f(a)=0$, $g(b)=0$, $f^prime(a)=0$. Prove that there exists $cin(a,b)$ such that
$$f''(c)g(c)+f(c)g''(c)+f'(c)g'(c)=0$$



I found that if we denote by $h(x)=f''(x)g(x)+f(x)g''(x)+f'(x)g'(x)$, we have that $h$ has the intermediate value property and, also, $h(a)leq 0$ and $h(b)>0$. I'm stuck only if $h(a)=0$.










share|cite|improve this question









$endgroup$












  • $begingroup$
    Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
    $endgroup$
    – GReyes
    Jan 17 at 22:40










  • $begingroup$
    I'm afraid I am
    $endgroup$
    – Andrew V
    Jan 17 at 23:25














0












0








0





$begingroup$


Let $f,g:[a,b]tomathbb{R}$ both increasing, twice differentiable and $g$ is also convex, $f(a)=0$, $g(b)=0$, $f^prime(a)=0$. Prove that there exists $cin(a,b)$ such that
$$f''(c)g(c)+f(c)g''(c)+f'(c)g'(c)=0$$



I found that if we denote by $h(x)=f''(x)g(x)+f(x)g''(x)+f'(x)g'(x)$, we have that $h$ has the intermediate value property and, also, $h(a)leq 0$ and $h(b)>0$. I'm stuck only if $h(a)=0$.










share|cite|improve this question









$endgroup$




Let $f,g:[a,b]tomathbb{R}$ both increasing, twice differentiable and $g$ is also convex, $f(a)=0$, $g(b)=0$, $f^prime(a)=0$. Prove that there exists $cin(a,b)$ such that
$$f''(c)g(c)+f(c)g''(c)+f'(c)g'(c)=0$$



I found that if we denote by $h(x)=f''(x)g(x)+f(x)g''(x)+f'(x)g'(x)$, we have that $h$ has the intermediate value property and, also, $h(a)leq 0$ and $h(b)>0$. I'm stuck only if $h(a)=0$.







real-analysis derivatives definite-integrals






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share|cite|improve this question










asked Jan 17 at 20:28









Andrew VAndrew V

30911




30911












  • $begingroup$
    Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
    $endgroup$
    – GReyes
    Jan 17 at 22:40










  • $begingroup$
    I'm afraid I am
    $endgroup$
    – Andrew V
    Jan 17 at 23:25


















  • $begingroup$
    Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
    $endgroup$
    – GReyes
    Jan 17 at 22:40










  • $begingroup$
    I'm afraid I am
    $endgroup$
    – Andrew V
    Jan 17 at 23:25
















$begingroup$
Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
$endgroup$
– GReyes
Jan 17 at 22:40




$begingroup$
Are you sure you do not have a coefficient "2" in front of $f'(c)g'(c)$?
$endgroup$
– GReyes
Jan 17 at 22:40












$begingroup$
I'm afraid I am
$endgroup$
– Andrew V
Jan 17 at 23:25




$begingroup$
I'm afraid I am
$endgroup$
– Andrew V
Jan 17 at 23:25










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