Supplementary Angles
Supplementary Angles
Supplementary 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 Angles
Angles of 100° and 80° are supplementary angles.
100° + 80° = 180°
How to Find a Supplementary Angle
Question
What is the missing angle θ below?
Step-by-Step:
1
The 56° angle and θ are supplementary angles. They add up to 180°.
56° + θ = 180°
2
Subtract the 56° angle from 180°.
θ = 180° − 56° = 124°
Answer:
The missing angle θ is 124°.
See Also
What is an angle? What is a straight angle? The interior angles of a polygon The exterior angles of a polygon What is a right angle? What is an acute angle? What is an obtuse angle?Interactive Test
show
Here's a second test on supplementary angles
Here's a third test on supplementary angles
Top Tip
What Types of Angles Are Supplementary?
Supplementary angles form a Straight line.
Note
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 Angles
Supplementary angles can either be:
-
both right angles
-
an acute angle and an obtuse angle.
