Describe in words the region of R3 represented by the equation. x2 + y2 = 49 Here x2 + y2 = 49 with no restrictions on, so a point in the region must lie on a circle of radius and center on the -axis, but it could be in any horizontal plane = k (parallel to the -plane). Thus, the region consists of all possible circles x2 + y2 = 49, = k and is therefore a with radius whose axis is the -axis.
