Geometry Foundations: Points, Lines, Planes, and Angles

Comprehensive vocabulary flashcards covering the fundamental concepts of points, lines, planes, and angle relationships based on classroom notes.

Point

Names a location and has no size; it is represented by a dot and named by a capital letter, such as $P$.

Line

A straight path that has no thickness and extends forever; named by a lowercase letter or two points on the line.

Plane

A flat surface that has no thickness and extends forever; named by a script capital letter or three points not on a line, such as plane $ABC$.

Coplanar

Points that lie in the same plane.

Collinear

Points that lie on the same line, such as points $K$, $L$, and $M$.

Segment (or Line Segment)

The part of a line consisting of two points, called endpoints, and all points between them; denoted as $AB$ or $BA$.

Endpoint

A point at one end of a segment or the starting point of a ray.

Ray

A part of a line that starts at an endpoint and extends forever in one direction.

Opposite Rays

Two rays that have a common endpoint and form a line.

Congruent Segments

Segments that have the same length.

Segment Bisector

Any ray, segment, or line that intersects a segment at its midpoint and divides it into two equal parts.

Angle

A figure formed by two rays, or sides, with a common endpoint called the vertex.

Vertex

The common endpoint of the two rays that form an angle; plural is vertices.

Adjacent Angles

Two angles in the same plane with a common vertex and a common side, but no common interior points.

Linear Pair

A pair of adjacent angles whose noncommon sides are opposite rays; for example, $\text{angle } 3$ and $\text{angle } 4$.

Complementary Angles

Two angles whose measures have a sum of $90^\text{o}$.

Supplementary Angles

Two angles whose measures have a sum of $180^\text{o}$.

Vertical Angles

Two nonadjacent angles formed by two intersecting lines; vertical angles are congruent.