Solve this:
Q. Given that : $i_1=r_2 and r_1=i_2$.
Then prove that ABE is parallel to FCD.

There is a simple concept of parallel lines called alternative exterior angles(if you don't know what is it then do check out on google). If alternate exterior angles are equal then two given lines are parallel. In this case lets see I1 and R2. They are alternate exterior angles. And it is already given that I1 =R2. Hence these two lines are parallel. I hope you get it.