Geometry Definitions
Straight Angle
Exactly 180 degrees
Line
Infinite set of points; extends infinitely in two directions
Congruent
Same size and shape
Bisector of a Segment
A line or ray that passes through the midpoint of a segment
Relationship Between Two Points
Always collinear; Exactly one line that contains them both; Always coplanar; Infinite planes that connect them both
Congruent Angles
Angles with the same measure
Acute Angle
Between 0 and 90 degrees
Obtuse Angle
Between 90 and 180 degrees
Adjacent Angles
Coplanar angles that share a common vertex and a common side, but have no interior points in common.
Bisector of an Angle
Divides it into two congruent angles
Right Angle
Exactly 90 degrees
Plane
Flat surface extending infinitely in all directions
Point
Location; no size or shape; 0-dimensional
Postulate
Mathematical statement accepted without proof
Line Segment
Part of a line; two endpoints and all the points inbetween
Ray
Piece of a line with a beginning and no end; one endpoint; extends infinitely in one directions
Non-Collinear Points
Points not on the same line
Non-Coplanar Points
Points not on the same plane
Collinear Points
Points on the same line
Coplanar Points
Points on the same plane
Congruent Segments
Segments with the same length
Relationship Between Four Points
Sometimes collinear; Sometimes coplanar; Sometimes coplanar but not collinear; sometimes non-coplanar; Four non-coplanar points determine space
Relationship Between Three Points
Sometimes collinear; Sometimes coplanar; Three non-collinear points determine a plane
Midpoint of a Segment
The point that divides a segment into two congruent segments
Space
The set of all points
Angle
The union of two rays with a common endpoint (vertex)
