# Mean Value Theorem (another)

Does the mean value theorem also apply to lateral derivatives?

Let $f: [a,b] \longrightarrow \mathbb{R}$ continuous and $f$ right differentiable in $(a,b)$, then, theres exists $c \in (a,b)$ such that $$f'_{+}(c) = \frac{f(b)-f(a)}{b-a}$$

In the proof of the Means Value Theorem, based on Rolle's Theorem, it wasn't clear to me what would happen if we changed this hypothesis

$f(x) = |x|$
Take $a=-1$, $b=1$, but there is no right tangent with slope $f'_{+}(x)=0$.
Consider the function f(x) = $2-|x|$ on $[-2,2].$
It is continuous and right differentiable but there is no point in $(-2,2)$ with $f'_{+}(c) = \frac{f(b)-f(a)}{b-a}=0$\$