Exercise $2$ Let $f$:$R^{2}R$ differentiable. Define

$h$:$(r,)|f(rcos(),rsin()).$

Explain why $h$ is differentiable. Compute $\frac{\text{d}\text{e}\text{l}\text{h}}{\text{d}\text{e}\text{l}\text{r}}(r,)$ and $\frac{\text{d}\text{e}\text{l}\text{h}}{\text{d}\text{e}\text{l}}(r,).$