Prove the following Theorem. The Euclidean Parallel Postulate is equivalent to the following statement: If a line is perpendicular to one of two parallel lines, then it is perpendicular to the other.

I have already been able to prove thatif a line is perpendicular to one of two parallel lines, then it is perpendicular to the otherby assuming that the Euclidean Parallel Postulate is true and arriving at a contradiction (indirect proof).

I am having trouble proving the Euclidean Parallel Postulate by assuning thatif a line is perpendicular to one of two parallel lines, then it is perpendicular to the otheris true.

Thanks in advance