Describe, in words or a graph, the region in 3 D space represented by the equation z = x.
Solution:
The solution of the equation z = x is the set of all points { (x,y,x) } where x and y are arbitrary.
Geometrically, this is a plane that makes a 45 degree angle with the x-y plane. The graph below
is plotted for -3 <= x < =3 and -5 <= y <= 5.