Let be a line and be a point not on . Through , draw a line parallel to . Now join to any point on . Choose any other point on . Through , draw a line parallel to . Let this meet at . What shape do the two sets of parallel lines enclose?
Follow the steps given in question for constructing the figure:
In figure, and
In opposite sides are parallel so they form a parallelogram.
Hence, a parallelogram is enclosed between line and .