Supplementary angles are two angles whose measures have a sum of 180°. Each angle is the supplement of the other.
Supplementary angles can be adjacent or nonadjacent.
Two adjacent oblique angles make up straight angle POM below.
The two angles are supplementary so, we can find the measure of angle PON,
|∠PON + 115° = 180°|
|∠PON = 65°|
For polygons, such as a regular pentagon ABCDE below, exterior angle GBC and its interior angle ABC are supplementary since they form a straight angle ABG. This is true for all exterior angles and their interior adjacent angles in any convex polygon.
Regardless of how wide you open or close a pair of scissors, the pairs of adjacent angles formed by the scissors remain supplementary. Below, angles FCD and GCD are supplementary since they form straight angle FCG.