Chapter 12 - Section 12.1 - Three-Dimensional Coordinate Systems - 12.1 Exercises - Page 797: 37

All points on or within the cylinder centered on the y-axis with radius 3.

Start with our cylinder, $x^2 + z^2 \leq r^2$ Radius: $r= 3$ We have found the radius, but have not accounted for the bounds set by the inequality. We want to account for all points $r \leq 3$. This tells us we are working with all points on or within our cylinder.