Section 1.2 Points, Lines, and Planes Chapter 1 Section 1.2 Points, Lines, and Planes

To define it or not to define it Definition: Using known words to define a new word Undefined terms: When a term is not given a definition Points, Lines, and Planes are all undefined terms Mathematicians do not choose to define what they are

Undefined terms Point Line Plane Something with no dimension Something that extends forever in one dimension Plane Something that extends forever in two dimensions •

Defined Terms Collinear Points Coplanar Points Intersect Intersection Points that lie on the same line Coplanar Points Points that lie in the same plane Intersect Two or more geometric figures are said to intersect if they have one or more points in common Intersection Set of points the figures have in common

Defined Terms Line Segment Ray A piece of a line cut off by two end points Ray All the points on one side of a given point called the initial point Initial Point

Use two points on the line and draw a line above them Symbolization • A B Use two points on the line and draw a line above them Lines Rays A • B Use the initial point and any other point on the ray then draw a ray on top Opposite Rays: Two rays that have the same initial point but extend in opposite directions