# 1 1 Understanding Points Lines and Planes Understanding

• Slides: 10

1. 1 Understanding Points, Lines, and Planes

Understanding Points, Lines, and Planes � Undefined terms- words that cannot be defined by using other figures ◦ Point- has no size or dimension; names a location ◦ Line- straight path that has no thickness, extends forever in two directions ◦ Plane- flat surface that has no thickness, extends forever in two dimensions

� Collinear- 3 or more points on the same line � Coplanar- 3 or more points on the same plane

� Segment (line segment) – part of a line, contains two points and all of the points between them � Endpoint- points on the end of a segment or the starting point on a ray

� Ray- part of a line, starts at an endpoint and extends forever in one direction � Opposite ray- two rays that have a common endpoint and extend in opposite directions forming a line

Examples: 1) a) Name 3 different segments b) Name the line 2 ways c) Name 4 different rays

Examples: 2) a) Name 4 points that are coplanar b) Name 4 points that are not coplanar c) Name 3 points that are collinear

Potulates � (1. 1. 1) Two points determine a line � (1. 1. 2) Three noncollinear points determine a plane � (1. 1. 3) If two points are in a plane, then the line containing the points is also in the plane

� (1. 1. 4) Two lines intersect at exactly one � (1. 1. 5) Two planes intersect at exactly one point line

Examples: � 3) Sketch two lines intersecting at exactly one point � 4) Sketch two lines intersecting a plane at two points