Question

In ΔABC, AB = AC and ∠A = 100°, then ∠C is equal to ______.

Options

• 30°

• 35°

• 40°

• 80°

Answer 1

In ΔABC, AB = AC and ∠A = 100°, then ∠C is equal to 40°.

Explanation:

AB = AC so triangle ABC is isosceles and the base angles ∠B and ∠C are equal.

The angles sum to 180°.

So, ∠B + ∠C

= 180° – 100°

= 80°

Hence, `∠C = 80^circ/2 = 40^circ`.

The fact that equal sides give equal base angles is standard for isosceles triangles.