Question

30. In ∆ ABC, BC = AB and ∠B = 80°. Then ∠A is equal to (A) 80° (B) 40° (C) 50° (D) 100°​

Answer 1

Answer:

Given: Δ ABC, BC = AB and ∠B = 80° As BC = AB

So it is an isosceles triangle.

Let ∠C = ∠A = x ∠B = 80° (given)

As we know, 

∠A + ∠B + ∠C = 180°

⇒ x + 80° + x = 180°

⇒ 2x = 180° - 80°

⇒ 2x = 100°

⇒ x = 50° So, ∠C = ∠A = 50°

Hence, option C is correct.

Answer 2

Given: Δ ABC, BC = AB and ∠B = 80° As BC = AB

So it is an isosceles triangle.

Let ∠C = ∠A = x ∠B = 80° (given)

As we know,

∠A + ∠B + ∠C = 180°

⇒ x + 80° + x = 180°

⇒ 2x = 180° - 80°

⇒ 2x = 100°

⇒ x = 50° So, ∠C = ∠A = 50°

Hence, option C is correct.