Describe and sketch the surface in 3 dimensional R^3 represented by the equation x^2 +z^2 =9

Answer 1

Notice that there is no y term, so y can be any value
x^2 + z^2 = 9 is a circle in the xz plane with a radius of 3
We are then "pushing this along the y-axis, resulting in a cylinder with radius 3
carefully type in (x^2) + (z^2) = 9 into
https://www.geogebra.org/3d?lang=en
to see the cylinder.