Since two of the sides are shown as being congruent, the base angles are the same. We are given the top angle, which is 98 degrees. All the angles of a triangle add up to 180. We can subtract 98 from 180, giving us 82, and divide that by two (since the base angles are congruent), giving us a measure of 41 degrees for each of the bottom angles of the isosceles triangle.
