5.3 The Fundamental Theorem of Calculus/10

${\begin{aligned}g(r)=\int _{0}^{r}{\sqrt {x^{2}+4}}dx\\[2ex]{\frac {d}{dx}}\int _{0}^{r}{\sqrt {x^{2}+4}}dx\\[2ex]{\sqrt {r^{2}+4}}dx-sqrt{0^{2}+4}dx\end{aligned}}$