Question

Name a pair of parallel lines other than the pair in Exercise 9. Why must they be parallel?

Short answer

Line$\overline{\mathrm{BH}}$ is parallel to line$\overline{\mathrm{CI}}$ as they form a pair of same side interior angles.

Step-by-step solution

Step 1. Highlight ∠BEF and ∠EFC.

Step 2. Description of step.

If a line intersect two lines and it makes two angles on the same side such that sum of two angles is equal to $180°$, then the lines are parallel and that line is transversal of two parallel lines.

Step 3. Description of step.

From the figure it can be observed that $\angle BEF$and $\angle EFC$are same side interior angles, as

width="211" height="44" role="math">m∠BEF+m∠EFC=90+90=180

Therefore, lines$\overline{BH}$ and$\overline{CI}$ are parallel.