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Basic Definitions
Geometry
Point
 Represented by a dot
 Location only, has no dimension
 Most basic form of geometry
Line
 Straight
 Consists of an infinite number of points
 Need 2 points to define a line
 Has no end points (goes on forever in both directions)
Endpoint
 A point on a line that signifies the line stops at that point
Ray
 A piece of a line
 Has one end point and extends forever in only one
direction
Line Segment
 A smaller piece of a line
 Has 2 endpoints
 Only type of line you can measure for distance
Length
 The measure of distance between two points
Midpoint
 Exactly half way between to points
 Usually only used for line segments
Parallel Lines
 Two or more distinct lines that never intersect
 Always stay the same distance apart
Perpendicular lines
 Two lines that intersect a right angle
 Right angle = 90°
Vertex
 The point at which two lines intersect
 The “pointy” part of an angle
Collinear
 2 or more points that are on the same line
 2 points that are not on the same line: non-collinear
Plane
 A flat, 2-dimensional surface
 Need 3 points or 2 intersection lines to define
 Examples: your paper, the whiteboard, the floor
Coplanar
 Points or lines that lie in the same plane
 If they don’t: non-coplanar
Space
 Any 3-dimensional area
 Examples: This room, the world, the universe
Skew Lines
 2 lines that do not intersect, however are going in
different directions
 What are 2 lines that do not intersect that are going in
the same direction?