Question

Consider the following function. f(x) = 9 − x2/3 Find f(−27) and f(27). f(−27) = f(27) = Find all values c in (−27, 27) such that f '(c) = 0. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) c = Based off of this information, what conclusions can be made about Rolle's Theorem? This contradicts Rolle's Theorem, since f is differentiable, f(−27) = f(27), and f '(c) = 0 exists, but c is not in (−27, 27). This does not contradict Rolle's Theorem, since f '(0) = 0, and 0 is in the interval (−27, 27). This contradicts Rolle's Theorem, since f(−27) = f(27), there should exist a number c in (−27, 27) such that f '(c) = 0. This does not contradict Rolle's Theorem, since f '(0) does not exist, and so f is not differentiable on (−27, 27). Nothing can be concluded.

Answer 1

I guess the function is $f(x)=9-x^{2/3}$. Then $f(-27)=0$ and $f(27)=0$.

The derivative is $f'(x)=-\dfrac23 x^{-1/3}$, but there is no $c$ such that

$-\dfrac23c^{-1/3}=0$

This doesn't contradict Rolle's theorem because $f'(0)$ does not exists. In other words, $f$ is not differentiable on (-27, 27), so the conditions of Rolle's theorem are not met. (Looks like that would be the last option, or the second to last option if the last one is "Nothing can be concluded")