Question

In a Δ ABC, if AB = AC and BC is produced to D such that ∠ACD = 100°, then ∠A =

A. 20°

B. 40°

C. 60°

D. 80°

Answer 1

∠ACB + ∠ACD = 180°

On solving we get,

∠ACB = 80°

∠ABC = ∠ACB = 80° (Angles opposite to equal sides are equal)

In ΔABC,

∠A + ∠B + ∠C = 180°

∠A + 80° + 80° = 180°

∠A = 20°