Draw a line segment AB of in length. Draw a line perpendicular to AB through A and B, respectively. Are these lines parallel?
Draw a line perpendicular to AB through A and B
Draw and considering A as the centre, draw an arc, cutting at . Considering as a centre and the same radius, draw an arc cutting the arc drawn at and then Considering as a centre and the same radius, draw an arc, cutting the arc drawn at
Considering as the centre and the same radius, draw an arc, cutting the arc drawn at and Draw and produced it to C and D.
Similarly we can draw the line perpendicular through
Thus, the given lines are parallel because the sum of the interior angles on the same side of the transversal is .