Question

In $\Delta ABC,BC=AB$ and $\angle B={80}^o.$ Then $\angle A$ is equal to

• A. ${80}^o$
• B. ${40}^o$
• C. ${50}^o$
• D. ${100}^o$

Answer 1

The correct option is C ${50}^o$

Given, $BC=AB$ and $\angle B={80}^o$

In $△ABC$, we have

$\angle A+\angle B+\angle C=180$.....(1) (Sum of all the angles in triangle is ${180}^o$)

$BC=AB$
$\Rightarrow \angle A=\angle C$ .......... [Angles opposite to equal sides are equal]

and $\angle B={80}^o$.....(2)
From (1) and (2), we get
$2\angle A=100$
$\therefore \angle A={50}^o$