I don't really understand what these two questions are asking. Nor do I know how to start it.
1) Describe in words the region of $\mathbb {R}^3$ represented by: $x^2 + z^2 \le 9$.
2) Write an inequality to describe: The solid upper hemisphere of the sphere of radius 2 centered at the origin.
Can some please explain what I am supposed to do here? Thanks in advance.