An Introduction to: Geometry By Wendy Bacon

Terms and Definitions . . .

Plane A flat surface Continues infinitely in all directions Labeled with a Capital Letter Example: Plane P P

Point • D A position in a plane Labeled with a Capital Letter Example: Point D • D

Line • A straight path of points B • A straight path of points Continues infinitely in both directions Can be determined by any two of its points Named by any two of its points Example: AB

Line Segment Part of a line Has two endpoints C D Segment Part of a line Has two endpoints Named by the two endpoints Example: CD

Ray Part of a line Has one endpoint G Part of a line Has one endpoint Continues infinitely in the other direction Named by the endpoint and one other point Example: FG

Angle Formed by two rays with a common endpoint J K Formed by two rays with a common endpoint Named by any three points One point from one ray The common endpoint One point from the other ray The common endpoint must be named in the middle Example: < IJK

Vertex The end point of an angle The middle point of the angle name J K The end point of an angle The middle point of the angle name This vertex is Point J

Intersecting Lines • Meet at a point MN and QR intersect at Point L R

Perpendicular Lines Intersect to from right angle W X WX YZ Y Z

Parallel Lines Must be in the same plane Never intersect Are the same distance apart at all points S T Q R Example: QR | | ST

Polygon A closed figure Lies within a plane J K L N M Polygon A closed figure Lies within a plane Sides are made up of line segments Named by its vertices in the order that they appear Example: Polygon JKLMN

Polygon A closed figure Lies within a plane Q R S T U V Polygon A closed figure Lies within a plane Sides are made up of line segments Named by its vertices in the order that they appear Example: Polygon QRSTUV

Polygon Polygon A closed figure Lies within a plane Q R S T U V J K L N M Polygon Polygon A closed figure Lies within a plane Sides are made up of line segments Named by its vertices in the order that they appear Example: Polygon QRSTUV Example: Polygon JKLMN