Geometry Vocab

Point

Undefined. A location. Has no size.

Line

Undefined. Straight path that extends in two opposite directions without direction and has no thickness.

Collinear Points

Points that lie on the same line.

Ray

The part of a line that consists of one endpoint and all the points of the line on one side of the endpoint.

Plane

Undefined. A flat surface that extends without end and has no thickness.

Parallel Lines

Lines that lie in the same plane and do not intersect.

Perpendicular Lines

Lines that intersect and form right angles.

Angle

Formed by two rays with the same endpoint. The rays are the sides and the common endpoint is the vertex.

Right Angle

An angle whose measure is 90.

Acute Angle

An angle whose measure is less than 90.

Obtuse Angle

An angle whose measure is between 90 and 180.

Adjacent Angles

Two coplanar angles that have a common side and a common vertex but no common interior points.

Complementary Angles

Angles that add up to be 90.

Supplementary Angles

Two angles that add up to be 180.

Linear Pair

A pair of adjacent angles whose non common sides are rays.

Vertical Angles

Two angles whose sides form two pairs of opposite rays.

Midpoint of a Segment

The point that divides the segment into two congruent segments.

Bisector

A ray that divides an angle into two congruent angles.

Theorem

A conjecture that is proven.

Postulate

An accepted statement of fact.