Two angles are supplementary angles when the sum of their measures is 180^(∘). In the diagram, ∠ B and ∠ E are supplementary because the sum of their measures equals 180^(∘). m ∠ B + m ∠ E = 180 ^(∘) 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.