If a line is perpendicular to each of two intersecting lines at their point of intersection, then the line is perpendicular to the plane determined by the two intersecting lines.

Through a given point there passes one and only one plane perpendicular to a given line.


If two planes are perpendicular to the same line, the planes are parallel.

Two lines perpendicular to the same plane are coplanar.

If a line is perpendicular to a plane, then any line perpendicular to the given line at its point of intersection with the given plane is in the given plane.

Two planes are perpendicular to each other if and only if one plane contains a line perpendicular to the second plane.

If a line is perpendicular to a plane, then every plane containing the line is perpendicular to the given plane.

If a plane intersects two parallel planes, then the intersection is two parallel lines.

The angle where two planes meet is called a dihedral angle.
Example: Carpenters and construction workers deal with dihedral angles when planning the construction of the trusses in a roof.
