Question

In $\Delta ABC,AB=AC$ and $\angle A={70}^o.$Then find the $\angle B$ and $\angle C.$

• A. ${75}^o$
• B. ${60}^o$
• C. ${55}^o$
• D. ${65}^o$

Answer 1

Answer: (C)

${55}^o$

Given, $AB=AC$ and $\angle A={70}^o$
$\therefore \Delta ABC$ is a isosceles triangle.
$\Rightarrow \angle B=\angle C$ ..... (side angle corresponding to equal sides are equal)
$\Rightarrow \angle A+\angle B+\angle C={180}^o$ ....(Angle sum property of triangle)
$\Rightarrow \angle A+2\angle B={180}^o$
$\Rightarrow {70}^o+2\angle B={180}^o$

$\Rightarrow 2\angle B=110$
$\Rightarrow \angle B=\frac{110}{2}={55}^o$