Angle relationships

transversal

A line that intersects two of more parallel lines

vertical angles

Opposite angles formed by two intersecting lines. Vertical angles are congruent.

linear pair

adjacent angles formed by intersecting lines; they are supplementary

straight angle

an angle that measures 180 degrees and forms a straight line

alternate interior angles

angles on opposite sides of the transversal and inside the parallel lines. They are congruent

alternate exterior angles

angles on opposite sides of the transversal and outside the parallel lines. They are congruent.

complementary angles

Two angles are complementary if the sum of their measures is 90 degrees

supplementary angles

Two angles are supplementary if the sum of their measures is 180 degrees.

same-side interior angles

When two lines are cut by a transversal, these angles are on the inside of the parallel lines on the same side of the transversal. They are supplementary.

same-side exterior angles

When two lines are cut by a transversal, these angles are outside the parallel lines on the same side of the transversal. They are supplementary.

corresponding angles

angles that have the same position on two different parallel lines cut by a transversal; they are congruent

adjacent angles

angles that share a vertex and a common side and do not overlap

parallel lines

lines in the same plane that never intersect or cross

perpendicular lines

lines that intersect to form right angles

exterior angle in a triangle

The angle formed by extending a side of a triangle. The exterior angle and its adjacent interior angle are supplementary. The measure of the exterior angle is equal to the sum of the other two measures in the triangle.