Question

The angles of a triangle are A, B and C.

Angle A is three times as big as angle B.
Angle B is half the size of angle C.
What is the size of angle A?

Answer 1

∠A = 90°

Explanation:

∠A = 3∠B

∠B = 1/2 × (∠C), this can also be written as ∠C = 2∠B

∠A + ∠B + ∠C = 180, because there are 180° inside a triangle

Write angle A, B and C in terms of angle B:

3 ∠B + ∠B + 2 ∠B = 180

Simplify:

6 ∠B = 180

∠B = 180 ÷ 6 = 30°

Work out angle A:

∠A = 3∠B = 3 × 30°

∠A = 90°