If a straight line is perpendicular to each of two other straight lines in a plane at their point of…

Straight line AB is perpendicular to the lines in plane MN at point B. "If from the foot of a perpendicular…

Two straight lines, AB and CD, perpendicular to the same plane (MN) are parallel.

Diagram used to prove the theorem: "A plane perpendicular to a radius at its extremity is tangent to…

Illustration of three intersecting planes. "The intersections of two parallel planes by a third plane…

Illustration of three intersecting planes. "The straight line perpendicular to one of two parallel lanes…

"If two angles not in the same plane have their sides respectively parallel and lying in the same direction,…

Two intersecting planes on a third plane. "If two intersecting planes are each perpendicular to a third…

"If two intersecting lines are each parallel to a given plane, the plane of these lines is parallel…

CD is the projection of AB upon OX. In each case AE=CD and AE=ABcos theta.

Illustration used to prove "Two angles whose sides are perpendicular each to each are either equal or…

"Let a represent a, b water, and c a piece of glass. The ray d, striking each medium in a perpendicular…

"Let the medium b be glass, and the medium c, water. The ray a, as it falls upon the medium b, is refracted…

A heraldic shield with a black surface, which is shown by the crossing horizontal and vertical lines.

The lines of contact are equal, but the axes are neither parallel to each other, or the line of contact.

Diagram used to prove the theorem: "Between two straight lines not in the same plane only one perpendicular…

Illustration of a leaning tower with a perpendicular drawn from the top of the tower to the ground to…

Illustration of a palm tree that is perpendicular to the ground. The tree is perfectly straight, as…

Triangle ABC with sides a,b,c labeled and angles A,B,C labeled and h labeled as height.

A test to ensure the triangle is accurate by drawing a perpendicular line from a T-square.

Illustration used to prove "The bisectors of the angles of a triangle are concurrent in a point which…

Illustration to show the bisector of the vertical angle of a triangle makes with the perpendicular from…

Triangle ABC with sides a,b,c labeled and angles A,B,C labeled and h labeled as height.

Illustration to show that the perpendicular bisector of the base of an isosceles triangle passes through…

Illustration used to prove "The perpendicular bisectors of the sides of a triangle are concurrent in…

Illustration to show the perpendiculars dropped from any point in the equilateral triangle to the three…

Illustration to show the perpendiculars dropped from the midpoint of the base to the legs of an isosceles…

Right triangle OCB that can be used to show the relationships between x, y, r, and Θ.