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If a function $f$ is $n$-times differentiable on $\mathbb R$ and $f^{(n)}=0$, prove $f$ is a polynomial of degree $\leq n-1$.

A hint would suffice.

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    @user9176 no I haven't2011-11-03

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Have you tried integrating? Start with the case $n=1$. Which functions have $0$ derivative? With the case $n=2$, which functions have $0$ second derivative? I think looking at it this way will make your life more easier.

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    Perhaps understanding the question is the first step to answering it :) maybe you are more familiar with the notation $f'(x) = 0$ and $f''(x) = 0$. Writing $f^{(1)} = 0$ is another way of saying that $f'(x) = 0$ for all $x$ in the domain of $f$. (In this case $\mathbb R$.)2011-11-03