Angle Types and Measurement

Pre-Algebra · Axiom Academy

LESSON Angle Types and Measurement An angle is just how far one ray has swung from another. Watch the opening grow, and every angle name falls into place. Hold one ray still and swing the other one open. The angle between them grows from 0° , and at each landmark it earns a new name. The size relative to a right angle ( 90° ) and a straight angle ( 180° ) is all that matters. 2. Complementary Angles Build a Corner Two angles are complementary when their measures add up to exactly 90° — together they "complete" a right angle. Watch a 35° angle and a 55° angle snap into the same corner. 30° + 60° = 90° 45° + 45° = 90° 25° + 65° = 90° 3. Supplementary Angles Build a Straight Line Two angles are supplementary when their measures add up to exactly 180° — together they straighten out into a single line. Here a 110° angle and a 70° angle meet along one ray. 120° + 60° = 180° 90° + 90° = 180° 110° + 70° = 180° You can now name any angle by how far it has opened, and recognize the two special pairs that build a corner and a straight line. Scroll up to revisit any step.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.