Perpendicular describes which geometric relationship?

• A. Parallel to a line, plane, or surface.
• B. At an angle of 45° to a line, plane, or surface.
• C. Coincident with a line, plane, or surface.
• D. At an angle of 90° to a line, plane, or surface.

Answer: (D)

Perpendicular describes a right-angle relationship between objects. When two geometric elements are perpendicular, they meet at an angle of 90 degrees. For a line and a plane, this means the line stands at a right angle to the plane, and, in the case of a line intersecting a plane, it is perpendicular to every line in the plane that it crosses. For two lines, perpendicular means the angle between them is 90 degrees. This distinguishes it from being parallel (0 degrees) or coincident (lying on top of each other), or from an angle like 45 degrees.