How to Graph the Intersection of Two Planes in 3D Coordinates using Mathematica?

[Mr Davis 97]

I have a simple Mathematica question, and I am not sure where to post it, so I'll just try to post it here. I am trying to graph the intersection of the planes y=3 and z=5 in 3D coordinates, but am not sure how.

 

[Orodruin]

ParametricPlot3D[{x,3,5},{x,-10,10}]

Exchange the 10s for whatever suits your plotting range.

 

[Mr Davis 97]

ParametricPlot3D[{x,3,5},{x,-10,10}]

Exchange the 10s for whatever suits your plotting range.

That works. As one additional question, how would I graph the curve $x^2 + z^2 = 9$ in three dimensions? Do I have to parametrize it, or can I use that equation directly?

 

[Orodruin]

That is a cylinder, not a curve. What is it you want to plot?