In the following video we use the chain rule to work
two problems:
A triangle is being squeezed so that its base $b$ is shrinking with
$\frac{db}{dt}=-1$ and its height is increasing with $\frac{dh}{dt}=1$.
At what rate is the area of the triangle changing when $b=3$ and
$h=5$?
Suppose that $w=xy+yz+xz$ and that $x = r\cos(\theta)$, $y=r\sin(\theta)$
and $z=r\theta$. Compute $\frac{\partial w}{\partial r}$ and
$\frac{\partial w}{\partial \theta}$ when $r=2$ and $\theta=\pi/2$.