There are two probabilities of the solution. First if 80° acts as one of the leg angles, second if 80° acts as the vertex angle.
FIRST PROBABILITY If 80° is one of the leg angles, then the other angle would be 80° too, because iscosceles has two congruent angles on the leg.
Find the vertex angle the sum of interior angles in a triangle is 180° vertex angle + angle on the leg + angle on the leg = 180° vertex angle + 80° + 80° = 180° vertex angle + 160° = 180° vertex angle = 180° - 160° vertex angle = 20° The interior angles are 80°,80°,20°
SECOND PROBABILITY If 80° is the vertex angle, we should find the value of the two leg angles. The two legs has congruent angles.
Find the leg angles the sum of interior angles in a triangle is 180° leg angle + leg angle + vertex angle = 180° 2 × leg angle + vertex angle = 180° 2 × leg angle + 80° = 180° 2 × leg angle = 180° - 80° 2 × leg angle = 100° leg angle = 50° The interior angles are 80°, 50°, 50°
