# Supplementary Angles (Mathematics Lesson)

# Supplementary Angles

Supplementary angles are two angles which add up to a straight angle.Two angles that add to 180° are are said to supplement each other.

# A Real Example of Supplementary Angles

Angles of 100° and 80° are supplementary angles.100° + 80° = 180°.

# How to Find a Supplementary Angle

**Question:**What angle supplements the 56° angle below?

**Step 1:**The 56° angle and θ are supplementary angles. They add up to 180°.

56° + θ = 180°.

**Step 2:**Subtract the 56° angle from 180°.

θ = 180° - 56° = 124°.

The supplementary angle is 124°.

# Another Real Example of Supplementary Angles

The slider below shows a real example of supplementary angles in mathematics; the interior and exterior angles of a polygon:##### Curriculum

##### Interactive Test

**show**

##### Top Tip

**WHAT TYPES OF ANGLES ARE SUPPLEMENTARY?**

**S**upplementary angles form a

**S**traight Line.

##### Note

**WHAT'S IN A NAME?**

Supplementary comes from the Latin word 'supplementum' meaning "filled up".

This is because an angle is filled up to form a straight line.

**SUPPLEMENTARY ANGLES CAN BE ACUTE, RIGHT AND OBTUSE**

Supplementary angles can either be:

- both right angles, or

- an acute angle and an obtuse angle.