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In geometry, pairs of angles can relate to each other in several ways.

In this lesson, we will learn

- about complementary angles
- about supplementary angles
- how to solve problems involving complementary and supplementary angles

Related Topics: More Geometry Lessons

Two angles are called **complementary angles** if the sum of their degree measurements equals 90 degrees (right angle). One of the complementary
angles is said to be the **complement** of the other.

The two angles do not need to be together or adjacent. They just need to add up to 90 degrees.
If the two complementary angles are adjacent then they will form a right angle.

∠ABC is the complement of ∠CBD |

**Example:**

*x* and *y* are complementary angles. Given *x* = 35˚, find the value *y*.

**Solution:**

* x *+ *y* = 90˚

35˚ + *y* = 90˚

*y* = 90˚ – 35˚ = 55˚

Worksheets for Complementary Angles

In a right triangle, the two acute angles are complementary. This is because the sum of angles in a triangle is 180˚ and the right angle is 90˚. Therefore, the other two angles must add up to 90˚. |

Two angles are called **supplementary angles** if the sum of their degree measurements equals 180 degrees (straight line) . One of the supplementary
angles is said to be the **supplement** of the other.

The two angles do not need to be together or adjacent. They just need to add up to 180 degrees. If the two supplementary angles are adjacent then they will form a straight line.

∠ABC
is the supplement of ∠CBD |

**Example:**

*x* and *y* are supplementary angles. Given *x* = 72˚, find the value *y*.

**Solution:**

* x *+ *y* = 180˚

72
˚ + *y* = 180˚

*y* = 180˚ –72˚ = 108˚

Worksheets for Supplementary Angles

A mnemonic to help you remember:

TheCinComplementary stands forCorner, 90˚

TheSinSupplementary stands forStraight, 180˚

Have a look at the following videos for further explanations of complementary angles and supplementary angles:

**How to identify and differentiate complementary and supplementary angles**.

This video describes complementary and supplementary angles with a few example problems. It will also explain a neat trick to remember the difference between complementary and supplementary angles.

**How to Find the Measure of Complementary Angles Using Algebra**

Complementary Word Problem

How to solve a word problem about its angle and its complement

The measure of an angle is 43 more than its complement. Find the measure of each angle.

What it means for angles to be complementary and supplementary and do a few problems to find complements and supplements for different angles.

Create a system of linear equations to find the measure of an angle knowing information about its complement and supplement.

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