In ∆ABC, BC = AB and ∠B = 80°. Then, ∠A = ?

Given: In ∆ABC, BC = AB and ∠B = 80°. 

In ∆ABC,

As, $A B=B C$

$\Rightarrow \angle A=\angle C$

Let $\angle A=\angle C=x$

Using angle sum property of a triangle,

$\angle A+\angle B+\angle C=180^{\circ}$

$\Rightarrow x+80^{\circ}+x=180^{\circ}$

$\Rightarrow 2 x=180^{\circ}-80^{\circ}$

$\Rightarrow 2 x=100^{\circ}$

$\Rightarrow x=\frac{100^{\circ}}{2}$

$\Rightarrow x=50^{\circ}$

$\Rightarrow \angle A=50^{\circ}$

Hence, the correct option is (a).