The thing about isosceles triangles is that when the sides are congruent to one another, the angles across from those congruent sides are also congruent. Because triangle angles measure 180 degrees and we have a 40 degree angle, we subtract 40 from 180 to get 140. Divide the result in half and that is the measure of one of the angles. In other words, PQR and PRQ are both 70 degrees.
