Question

For the given isosceles triangle, find $\angle B.$

• A. ${60}^o$
• B. ${59}^o$
• C. ${58}^o$
• D. ${57}^o$

Answer 1

The correct option is B ${59}^o$

For the given triangle,
AC = BC
$\therefore$ The opposite angles are equal.
$\Rightarrow \angle A=\angle B$


118° is the exterior angle at C.
$\therefore \angle ACB={180}^o–{118}^o={62}^o$

Sum of interior angles $={180}^o$

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

$\Rightarrow 2\angle B+{62}^o={180}^o$

$\Rightarrow \angle B=\frac{{180}^o–{62}^o}{2}=\frac{{118}^o}{2}={59}^o$