Points, Lines, and Planes

Geometry vocabulary and postulates based on the Points, Lines, and Planes lecture series.

Point

Thought of as a dot that represents (stands for) a specific location on a plane or in space, having zero dimensions and noted by a capital letter.

Line

A straight one-dimensional figure of infinite length containing at least two points, noted using two capital letters with a double arrow on top or a single lower-case cursive letter.

Collinear

A set of 3 or more points that are on the same line, noted by at least 3 capital letters separated by a comma.

Non-collinear

A set of three or more points that are on the same line, noted by at least 3 capital letters separated by a comma.

Line segment/segment

A piece of a line consisting of two points and all of the points in between, noted by two capital letters topped with a line with no arrows.

Ray

Extends forever in one direction and has exactly one endpoint; its notation consists of two capital letters with the endpoint listed first with a ray above them.

Opposite Rays

Two rays with the same endpoint that point in opposite directions, where both rays must be named with the same endpoint first.

Plane

Thought of as a flat surface that extends forever in all directions, having two dimensions (length and width); noted by a symbol resembling a squashed square with four non-collinear points or the word plane with an upper case script letter.

Coplanar

Points (at least 4) that lie on the same plane, listed with a comma between them.

Intersection

The point or set of points that two or more figures have in common.

Intersecting Planes

Planes that intersect along a line.

Space

A boundless three-dimensional set of all points that has length, height, and width.

Segment Addition Postulate

If $B$ is between $A$ and $C$, then $AB + BC = AC$.