Question

In an isosceles triangle, the vertex angle is 80° and the sides containing the vertex angle are equal. Find the measure of the base angles.

Answer 1

Let the base angle of the isosceles triangle is x.

Since the two sides of the isosceles triangle are equal, therefore its base angles are also equal.
By angle sum property of triangle, we know;

2x + 80 = 180
(1 mark)

⇒ 2x = 180 - 80

⇒ 2x = 100

⇒ x = 50
(1 mark)

Hence, the measure of each of the base angles is 50°.