# FTC problem

$f(x) = \int_{5}^{x^2} { \left( \frac{1}{5}t^2-1 \right) }^{8} \hbox{d} t$
If $\phi (x)$ is a differentiable function and
$f(x) = \int\limits_c^{\phi (x)} {g(t)dt} \quad \Rightarrow \quad f'(x) = \phi '(x)g(x).$