Supplementary Angles

What are Supplementary Angles?
Two angles are supplementary if they add up to 180°. Supplementary angles, when placed adjacent to each other, form a straight line, a 180° angle. Do note however that supplementary angles do not have to be adjacent to each other, they need only to have an angle measure sum of 180 degrees.

The following diagrams show examples of supplementary angles. Scroll down the page for more examples and solutions for supplementary angles.

 

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Key Characteristics of Supplementary Angles:
1. Sum is 180°:
If you have two angles, say Angle A and Angle B, they are supplementary if:
Measure of Angle A + Measure of Angle B = 180°

2. Linear Pair (when adjacent):
If two supplementary angles are placed next to each other (i.e., they share a common vertex and a common side), they form a linear pair. A linear pair always forms a straight line.

• More examples of Supplementary Angles

Supplementary Angles add up to 180 Degrees

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Supplementary Angles

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It is common to mix up supplementary and complementary angles. Here is a trick to help you remember which is which:

The “C” and “S” Trick
Complementary: Think C for Corner. A corner (like of a square or a table) is a right angle, which is 90 degrees.
Supplementary: Think S for Straight. A straight line forms a straight angle, which is 180 degrees.

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