Angles whose measures add up to 180°.
Example
In this figure, angles 2 and 3 are supplementary, as they form a straight angle.
The supplement of an 80° angle is a 100° angle, as 80 + 100 = 180.
In this figure, angles 2 and 3 are supplementary, as they form a straight angle.
The supplement of an 80° angle is a 100° angle, as 80 + 100 = 180.