Use limit theorems as neede to evaluate each of the following limits b) \

The figure shows the surface created when the cylinder ${\displaystyle y^2+Z^2=1}$ intersects the cylinder ${\displaystyle x^2+Z^2=1}$. Find the area of this surface.
The figure is something like:

Find the critical points of the following functions.Use the Second Derivative Test to determine (if possible) whether each critical point corresponds to a local maximum, a local minimum,or a saddle point. If the Second Derivative Test is inconclusive,determine the behavior of the function at the critical points.
${\displaystyle f(x,y)=\sin }$$(2\pi x)\cos (\pi y)$, for ${\displaystyle \left|x\right|\le \frac{1}{2}}$ and ${\displaystyle \left|y\right|\le \frac{1}{2}}$