Question

In ABC, if $BC=AB$ and $\angle B={80}^0$, then $\angle A$ is equal to :

• A. ${80}^0$
• B. ${40}^0$
• C. ${50}^0$
• D. ${100}^0$

Answer 1

Answer: (C)

${50}^0$

As $BC=AB$

$\Rightarrow \angle A=\angle C$ (As angles opposite to equal sides are equal)

Let the angles be $x$ each.

Now by using angle sum property of triangle

$\angle A+\angle B+\angle C={180}^{\circ }\Rightarrow x+{80}^{\circ }+x={180}^{\circ }\Rightarrow 2x={100}^{\circ }\Rightarrow x={50}^{\circ }$

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