Question

In $△ABC$, given that $\angle A={70}^o$ and $AB=AC$. Find the other angles of $△ABC$.

Answer 1

Let $\angle B=x^o$ and $\angle C=y^o$
Given that $△ABC$ is an isosceles triangle
$AC=AB$
$x^o=y^o$
In $△ABC$
$\angle A+\angle B+\angle C={180}^o$
${70}^o+x^o+y^o={180}^o$
${70}^o+x^o+x^o={180}^o$ [$\because$ $x^o=y^o$]
$2x^o={180}^o-{70}^o$
$2x^o={110}^o$
$x^o=\frac{{110}^o}{2}={55}^o$.
Hence $\angle B={55}^o$ and $\angle C={55}^o$