Basic Terms of Geometry

Basic Geometric Figures Undefined terms: ♥Line ♥Point ♥Plane

Point Points are often shown as dots, and represent a location. Think of ordered pairs on a coordinate plane. HOW TO WRITE: ♥ Points are named as ONE capital letter such as A or X A

Lines A line is made up of points, has no thickness, is perfectly straight, and has infinite length. HOW TO WRITE: ♥ Lines are named by two points (capital letters) on the line, with a double-headed arrow over the two letters. Or ♥ a single lowercase script letter if there are no points on the line m EFFE

Plane A plane extends infinitely in all directions along a flat surface. HOW TO WRITE: ♥ A plane can be named by three points (THREE capital letters) that lie in the plane but NOT on the same line. DEF Or ♥ It can be named by one script capital letter such as R. D E F R

Defined Terms

Collinear ♥Points on the same line Coplanar ♥Points on the same plane

Segment A segment is a part of a line that begins at one point and ends at another. The points are called the endpoints of the segment. ♥HOW TO WRITE: –The endpoints are capital letters and have a bar over them. »AB

Ray ♥A ray is a part of a line that starts at a point and goes forever in one direction. ♥The point is called the endpoint of the ray ♥HOW TO WRITE: Two capital letters with a ray on top. Always name with the endpoint FIRST. CD C D

Opposite rays ♥Opposite rays are two rays that share the same endpoint and form a line.. ♥Name the rays by their shared endpoint and any other point on each ray. TD C D T TC

Intersection ♥When you have two or more geometric figures, their intersection is the set of points the figures have in common. C D T m

1.The intersection of two lines is a ________ 2.The intersection of two planes is a ______. 3.Through any two points there is exactly one _______. 4.Through any three noncollinear points there is exactly one ______. Four Facts POINT LINE PLANE