2 lines that are intersected by a third line known as a transversal.

2 intersecting lines, one of which is vertical and one of which is horizontal. The intersection forms…

"Let any irregularly shpaed body, as a stone or chair, be suspended so as to move freely. Drop a plumb…

"The horizontal alignment Turn signs may be used in advance of situations where the horizontal roadway…

"The horizontal alignment Turn signs may be used in advance of situations where the horizontal roadway…

"The horizontal alignment Turn signs may be used in advance of situations where the horizontal roadway…

The lines which join corresponding points in an involution on a conic all pass through a fixed point;…

Illustration of a cylinder cut by a plane making an angle of 57° with the base.

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

Illustration of the intersection of a hexagonal pyramid and a plane.

Diagram depicting a cone with both nappes intersected by plane J to form a hyperbola.

The segments between the point of intersection of two tangents to a conic and their points of contact…

Diagram of a cone intersected by plane J to form a parabola. Also pictured is a circle formed by the…

Two planes lie perpendicular to one another. A line perpendicular to plane 1 and a line perpendicular…

"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 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.

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

Diagram used to prove the theorem: "If a pyramid is cut by a plane parallel to the base, the edges are…

Diagram used to prove the theorem: "Every section of a sphere by a lane is a circle."

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 straight lines are cut by three parallel planes, the corresponding segments are proportional."

"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…

Two parallel planes perpendicular to a line (AB). "A straight line perpendicular to one of two parallel…

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

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