Question

Find $\angle C$ in the figure if $\overline{AB}\parallel \overline{DC}$

Answer 1

$AB\parallel DC$ and $BC$ is the transversal.

So, $\angle B$ and $\angle C$ are angles on the same side of transversal.

$\Rightarrow$ $\angle B+\angle C={180}^o$ [ Interior angles on same side of transversal are supplementary ]

$\Rightarrow$ ${120}^o+\angle C={180}^o$

$\Rightarrow$ $\angle C={180}^o-{120}^o$

$\therefore$ $\angle C={60}^o$