Problem : Line AB is perpendicular to line CD. Line EF is perpendicular to line CD. What is the angle formed between line AB and line EF?

There is no angle formed: the lines are parallel.

Problem : When perpendicular lines intersect, how many pairs of supplementary angles are formed?


Problem : What is the shortest distance between two parallel lines?

A segment perpendicular to the parallel lines with an endpoint on each line represents the shortest distance between those lines.