Moving up or down off a flat plane requires a third axis and a third number to indicate how far a point is above or below the plane.

Question

Quizplus · Accepted Answer

In a three-dimensional space, moving up or down off a flat plane indeed requires a third axis (commonly the z-axis) and a third number to indicate the position's elevation relative to the plane. This is because the first two axes (x and y) only allow movement within the plane itself.

Moving Up or Down Off a Flat Plane Requires a Third