Straight Line, or Line
A line measuring 180º. Extends indefinitely in both directions.
Line Segment
A line segment has a finite length.
Parallel Lines
Lines that lie in a plane and never intersect.
Perpendicular Lines
Lines that intersect at a 90 angleº.
Intersecting Lines
Two lines that intersect, or cross, at a point.
Interior Angles of Intersecting Lines
The interior angles of two intersecting lines form a circle (360º)
Vertical Angles
The angles found opposite each other when two lines intersect; vertical angles are equal in measure.
Exterior Angle
An angle created by extending the line of a polygon beyond the vertex of that polygon.
Exterior Angle of a Triangle
The exterior angle of a triangle is equal to the sum of the two non-adjacent (or opposite) interior angles.
Transversal
A line that crosses, or cuts, two parallel lines; the transversal creates four angles where it crosses each parallel line, for a total of eight angles. All of the acute (or smaller) angles are equal and all of the obtuse (or larger) angles are equal. The sum of any acute angle and any obtuse angle is equal to 180º.
