Supplementary Angles
Two Angles are Supplementary if they add up to 180 degrees.
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These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°. Notice that together they make a straight angle. |
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But the angles don't have to be together.
These two are supplementary because 60° + 120° = 180° |
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If the two angles add to 180°, we say they "Supplement" each other.
Supplement comes from Latin supplere, to complete or "supply" what is needed. |
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Spelling: be careful, it is not "Supplimentary Angle" (with an "i") |
Complementary vs Supplementary
A related idea is Complementary Angles, they add up to 90°
How can you remember which is which? Easy! Think:
- "C" of Complementary stands for "Corner"
 (a Right Angle), and
- "S" of Supplementary stands for "Straight" (180 degrees is a straight line)
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