Angle BCD and angle ACB are supplementary because they form a straight line. This means they add up to 180. We can write an equation to model the situation:
m<BCD + m<ACB = 180
106 + m<ACB = 180
m<ACB = 74
Since we are given two sides of the triangle are congruent, the triangle is isosceles. The base angles of an isosceles triangle are congruent, so we can say:
