Any triangle has three angles whose measures add up to a total of 180°.
This triangle has two known angle measures. First, find the missing interior angle measure.
180 - (74 + 20)
180 - 94
86
The missing interior angle's measure is 86°. An exterior angle is supplementary to its adjacent interior angle, which means that the measure of the interior angle plus the exterior angle measure is 180.
180 - 86
94
Another way to find out a missing exterior angle measure is to simply add the measures of the two nonadjacent interior angles.
