Question

Show that if a straight line is perpendicular to one of the two or more parallel lines, then it is also perpendicular to the remaining lines.

Answer 1

Let AB and CD be two parallel lines. Let PQ be perpendicular to AB. We need to prove that PQ is also perpendicular to CD.

In the figure, angles NMB and MND are interior angles.

Therefore, PQ is also perpendicular to CD.