NCERT Class 9 Mathematics Textbook for Blind Students made Screen Readable by Professor T K Bansal.

Draw two different lines, Line PQ and Line RS on a paper. We will see that we can draw them in two different ways as shown in Figure 6.5 (i) and Figure 6.5 (ii).

Figure 6.5 (i) : Intersecting lines

Figure 6.5 (ii) : Parallel lines

Recall the notion of a line, that it extends indefinitely in both directions. Lines PQ and RS in Figure 6.5 (i) are intersecting lines and in Figure 6.5 (ii) are parallel lines. Note that the lengths of the common perpendiculars at different points on these parallel lines are the same. This equal length is called the distance between two parallel lines.