Illustration used to show "The two perpendiculars to the sides of an angle from any point in its bisector…

Illustration used to show "The two perpendiculars to the sides of an angle from any point not in its…

Illustration showing that from any point in the circumference of a circle, a chord and a tangent are…

Diagram used to prove the theorem: "Every point in a plane which bisects a dihedral angle is equidistant…

"If from the foot of a perpendicular to a plane a straight line is drawn at right angles to any line…

Illustration of perpendicular lines. Intersecting lines that meet at a right angle.

Illustration of perpendicular lines with the horizontal and vertical lines labeled. "A horizontal line…

"If two intersecting planes are each perpendicular to a third plane, their intersection is also perpendicular…

"If a straight line is perpendicular to each of two straight lines at their point of intersection it…

"If one of two parallels is perpendicular to a plane, the other is also."

"Through a given line oblique to a plane, one, and only one plane, can be passed perpendicular to the…

"If two planes are perpendicular to each other, a line in one of them perpendicular to the intersection…

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

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

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…