91Ó°ÊÓ

• $a$is transversal to parallel lines $c$and$d$
• $b$is transversal to parallel lines $c$and$d$
• $c$is transversal to parallel lines$a$and$b$
• $d$is transversal to parallel lines$a$and$b$

$∠15$is corresponding angle to $∠13$

Postulate 10: If two parallel lines are cut by a transversal then the corresponding angles are congruent

$\begin{array}{c}∠15â‰\dots ∠13\\ m∠15=m∠13\end{array}$

Thus,$m∠15=110$

$∠11$forms a linear pair with $∠15$, so sum of measurement of these two angles is 180

role="math" localid="1637671933532" $\begin{array}{c}m∠11+m∠15=180\\ m∠11+110=180\end{array}$

role="math" localid="1637671993754" $\begin{array}{c}m∠11=180−110\\ m∠11=70\end{array}$

$∠3$is a corresponding angle to$∠11$

Postulate 10: If two parallel lines are cut by a transversal then the corresponding angles are congruent

$\begin{array}{c}∠3â‰\dots ∠11\\ m∠3=m∠11\end{array}$

Thus,$m∠3=70$