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.
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.
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.