(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Describe in words the region of R3 represented by the inequality x^2 + z^2 <= 9

2. Relevant equations

Equation of a sphere= (x-h)^2 + (y-k)^2 + (z-l)^2 = r^2

3. The attempt at a solution

Since there is no y value in the given inequality, I stated that it would be points in or on a circle on the xz-plane with center at the origin, and the radius is 3 with respect to the xy-plane.

However, my book says this inequality describes a cylinder of radius 3 with y-axis. Can someone explain this to me please? How can it be a cylinder? And why is the radius with the y-axis and not with the xy-plane?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Describe this region of R3

**Physics Forums | Science Articles, Homework Help, Discussion**