#### Answer

A line l is perpendicular to plane A if l is perpendicular to all of the lines in plane A that intersect l. (Think of a stick standing straight up on a level surface. The stick is perpendicular to all of the lines drawn on the table that pass through the point where the stick is standing).
A plane B is perpendicular to a plane A if plane B contains a line that is perpendicular to plane A. (Think of a book balanced upright on a level surface.)

#### Work Step by Step

A plane is perpendicular to another plane when it has a line that is perpendicular to the other plane.