Question

In ∆ABC, AB = AC and ∠B = 50°. Then, ∠A = ?
(a) 40°
(b) 50°
(c) 80°
(d) 130°

Answer 1

In $△ABC$, we have:
AB = AC
∠B = 50°
Since ABC is an isosceles triangle, we have:
$\angle C=\angle B$
$\angle C=50°$
In triangle ABC, we have:
$$\begin{gathered} \angle A+\angle B+\angle C=180° \\ \Rightarrow \angle A+50+50=180° \\ \Rightarrow \angle A=180°-100° \\ \therefore \angle A=80° \end{gathered}$$
Hence, the correct answer is option (c).