Basics

Geometry

of

Geometry

Study Guides

Big Picture

Geometry is founded upon some very important basic concepts. These include points, angles, lines, and line segments.

There are many postulates that govern the way that we can use these basic concepts. After the basic foundation is

created, we can progress to harder, more advanced geometry.

Key Terms

Undefined Term: A term that cannot be mathematically defined using other known words. The undefined terms point,

line, and plane are the building blocks of geometry.

Point: Location that has no size (no dimension).

Line: Infinite series of points in a row (1-dimensional). It has direction and location and is always straight.

Plane: Any flat, 2-dimensional surface.

Undefined terms can be used to define other geometric terms:

Segment: Portion of a line that is ended by two points.

Ray: Portion of line that has only one endpoint and extends infinitely in the other direction.

Endpoint: Point at the end of a segment or at the start of a ray.

Space: Set of all points expanding in three dimensions. It has no shape and no limits.

Collinear: Points that lie on the same line.

Coplanar: Points or lines that lie within the same plane.

Intersection: Point or set of points where lines, planes, segments, or rays cross (intersect).

Postulate: Basic rule that we can assume to be true. Also known as an axiom.

Drawing and Labeling

Notation

Term

Diagram

A capital label (A, L, F)

Point

A lowercase letter (line g) or two points on the

Line

line (PQ or QP)

A script capital letter (plane M) or three points

Plane

not on a line (plane ABC)

Think of a plane as a huge sheet of paper!

The two endpoints (AB or BA)

Segment

Endpoint and any other point on the ray (CD)

Ray

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