Question

In a triangle ABC, $\angle A={80}^o$ and $AB=AC$, then $\angle B$ is ....................

• A. ${50}^o$
• B. ${60}^o$
• C. ${40}^o$
• D. ${70}^o$

Answer 1

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

In $△ABC$,

$\angle ABC=\angle ACB$ ( Equal sides $AB=AC$ have equal opposite angles)

$\angle A+\angle B+\angle C={180}^o$ (Sum of all theinterior angles of a triangle is ${180}^o$

$\Rightarrow {80}^0+2\angle B={180}^o$ [As $\angle A={80}^o$]

$\Rightarrow \angle B={50}^o$