y° = 2x° + 20° x° + x° + y° = 180° or y = 2x + 20 2x + y = 180 Substitute 2x + 20 for y in the second equation: 2x + (2x + 20) = 180 2x + 2x + 20 = 180 4x + 20 = 180 4x = 160 x = 40 Substitute 40 for x in y = 2x + 20 y = 2(40) + 20 y = 80 + 20 y = 100 So the base angles are 40° each and the vertex angle is 100° Edwin