Compute a derivative of a function defined by an integral If  $h$ is continous, and $f$ and $g$ are differentiable and 
$$F(x)=\int \limits_{f(x)}^{g(x)} h(t) dt$$ then f is differentiable and $F'(x) = h(g(x))g'(x) - h(f(x))f'(x)$

Hint : Just write that $\int_{f(x)}^{g(x)} h(t)dt = H(g(x))-H(f(x))$ where $H$ is a primitive of $h$. Then just use the chain rule.
