Vocabulary

Complementary angles are two angles that together form a right angle.​ The sum of two complementary angles is 90 degrees. ​

Supplementary angles are two angles that together form a straight angle.​ The sum of two supplementary angles is 180 degrees. ​

Concept

Find the supplement or complement of an angle.

Rules

Complementary angles are two angles that together form a right angle.​ The sum of two complementary angles is 90 degrees. ​
To find the missing complementary angle, subtract the given angle from 90 degrees.

Supplementary angles are two angles that together form a straight angle.​ The sum of two supplementary angles is 180 degrees. ​
To find the missing supplementary angle, subtract the given angle from 180 degrees.

Example

What is the supplement of an angle measuring 72°?

Solution

Supplementary angles add up to 180°. To find the supplement, find 180° - 72° = 108°.

Pre-requisite Skills

Lines (8.6.1)

Complementary and Supplementary Angles (7.8.3)

Angle Relationships (6.10.5)