# Undefined terms in Geometry

Topics: Euclidean geometry, Line, Line segment Pages: 2 (379 words) Published: November 4, 2013
﻿Geometry III

I. Undefined Terms
1. Point-though we represent a point with a dot, the point has no length, width, or thickness. A point is usually named with a capital letter. In the coordinate plane, a point is named by an ordered pair, (point A)  . A

2. LINE –In geometry, a line has no thickness but its length extends in one dimension and goes on forever in both directions. A line is depicted to be a straight line with two arrowheads indicating that the line extends without end in two directions. A line is named by a single lowercase written letter or by two points on the line with an arrow drawn above them A PBAB

• • •
Subsets of a Line
A. Line segment-A line segment is the portion of a line that includes two particular points and all points that lie between them, while a ray is the portion of a line that includes a particular point, called the end point, and all points extending infinitely to one side of the end point AB and PB

Between

-if AP+BP=AB
B. Ray-A ray is a part of a line that begins at a particular point (called the Endpoint) and extends endlessly in one direction. A ray is also called half-line.

3. Plane- plane has no thickness but extends indefinitely in all directions. Planes are usually represented by a shape that looks like a tabletop or wall. Even though the diagram of a plane has edges, you must remember that the plane has no boundaries. A plane is named by a single letter (plane m) or by three non-collinear points (plane ABC). II. Definition

Coplanar- A set of points, lines, line segments, rays or any other geometrical shapes that lie on the same plane are said to be Coplanar.

Collinear-Passing through or lying on the same straight line

POSTULATE or Axiom -accept w/o a proof
Postulate 1
Two point determine a line
AB

Postulate 2
3 collinear point...