Front

A pair of angles whose sum is 90 degrees

Back

Complementary angles

Front

Triangles that are scale drawings of each other. They have the same shape but may have a different size

Back

Similar triangles

Front

When two lines are cut by a transversal, a pair of angles on opposite sides of the transversal and between the two lines

Back

Alternate interior angles

Front

Lines that cross at a common point

Back

Intersecting lines

Front

When two lines are cut by a transversal, a pair of angles on opposite sides of the transversal and outside the two lines

Back

Alternate exterior angles

Front

A pair of angles whose sum is 180 degrees

Back

Supplementary angles

Front

Angles that are opposite each other when two lines intersect

Back

Vertical angles

Front

Lines that never intersect and are always the same distance apart

Back

Parallel lines

Front

An angle that measures more than 90 degrees but less than 180 degrees

Back

Obtuse angle

Front

An angle that measures less than 90 degrees

Back

Acute angle