Concept

Supplementary Angles

Two angles are supplementary angles when the sum of their measures is

18 0^{\circ} .

Applet showing two angles for which the sum of the measures is 90

In the diagram,

∠ B

and

∠ E

are supplementary because the sum of their measures equals

18 0^{\circ} .

m ∠ B + m ∠ E = 18 0^{\circ}

When using radians as the unit of measure, two angles are supplementary when the sum of their measures is

π,

or about

3.14,

radians.

m ∠ B + m ∠ E = π

If two angles are supplementary, either both are right angles or one is acute and the other obtuse. When two supplementary angles are adjacent, they are called a linear pair or straight angle pair. Notice that a linear pair forms a straight angle.

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