Basic Geometry Definitions

A figure formed by two rays that share an endpoint.

• opposite rays

• angle

• vertical angles

• vertex

Points that lie on the same plane.

• coplanar

• collinear

• intersection

• line

Adjacent angles that are supplementary.

• perpendicular

• linear pair

• complementary

• congruent

Two angles that share a common side and vertex but do not overlap.

• complementary angles

• supplementary angles

• perpendicular lines

• adjacent angles

A segment, line or plane that divides an angle or segment into two equal parts.

• midpoint

• segment

• bisector

• congruent

A measurable part of a line.

• length

• ray

• line segment

• angle

A part of a line that extends indefinitely in one direction.

• ray

• line segment

• plane

• line

The common endpoint of an angle. (Where the sides intersect)

• vertex

• interior

• adjacent

• right

Two angles directly across from each other on intersecting lines.

• linear pair

• supplementary

• complementary

• vertical angles

An angle that measures less than 90 degrees.

• acute

• right

• obtuse

• straight