The LessonSupplementary angles are two angles which add up to a straight angle (180°).Two angles that add to 180° are are said to supplement each other.
A Real Example of Supplementary AnglesAngles of 100° and 80° are supplementary angles.
100° + 80° = 180°
How to Find a Supplementary Angle
QuestionWhat is the missing angle θ below?
The 56° angle and θ are supplementary angles. They add up to 180°.
56° + θ = 180°
Subtract the 56° angle from 180°.
θ = 180° − 56° = 124°
Answer:The missing angle θ is 124°.
Lesson SlidesThe slider below shows another real example of supplementary angles. Open the slider in a new tab
What Types of Angles Are Supplementary?Supplementary angles form a Straight line.
What's In an Name?Supplementary comes from the Latin word "supplementum" meaning "fill up, complete, supply". This is because an angle is filled up to form a straight line. We get the word "supply" from the same root.
Supplementary Angles Can Be Acute, Right and Obtuse AnglesSupplementary angles can either be:
- both right angles
- an acute angle and an obtuse angle.