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Geometry · Quick Reference

Angles Cheat Sheet

Geometry · Lesson 3/16
In one line: an angle forms when two rays share a common endpoint — measuring how much one ray has rotated from the other, in degrees.

Key Ideas

1Angle Definition. Formed by two rays sharing a common endpoint (the vertex), measured in degrees.
2Types of Angles. Acute (less than 90°), right (exactly 90°), obtuse (between 90° and 180°), straight (exactly 180°).
3Complementary Angles. Two angles whose measures add up to exactly 90°.
4Supplementary Angles. Two angles whose measures add up to exactly 180°.
5Vertical Angles. The pair of opposite angles formed when two lines cross; vertical angles are always equal to each other.

Worked Examples

An angle measures 35°. Find its complement.
55°
An angle measures 110°. Find its supplement.
70°
Classify a 95° angle.
Obtuse angle

Formulas

Complementary angles sum to 90°
Supplementary angles sum to 180°

Practice Yourself

Find the complement of a 40° angle.
50°
Find the supplement of a 130° angle.
50°
Classify a 45° angle.
Acute