Definition: Supplementary angles are two angles whose measures add up to 180 degrees, and together they form a straight line when placed side by side.
What are supplementary angles?
Two angles are supplementary if their measures sum to 180 degrees. They do not need to touch.
How do you find a missing angle?
Subtract from 180. If one angle measures 117 degrees, the other is 180 – 117 = 63 degrees.
When do they appear?
A straight line makes a straight angle of 180 degrees. Any ray from a point on the line splits it into two supplementary angles, called a linear pair. If a robot arm at an angle of x degrees to the floor extends and the other side is (2x + 30) degrees, then x + 2x + 30 = 180. So 3x = 150, giving x = 50, and the angles are 50 and 130.
How do they relate to other angles?
Two obtuse angles can never be supplementary, since each exceeds 90 and their sum would exceed 180. Two right angles are supplementary.
What is a common mistake?
Mixing up supplementary and complementary. The word straight begins with s, like supplementary, and a straight angle is 180 degrees.