NCERT Book Class 7 Mathematics (Part I) Chapter 5 Parallel and Intersecting Lines

PARALLEL AND
5 INTERSECTING
LINES

5.1 Across the Line
Take a piece of square paper and fold it in different ways. Now, on
the creases formed by the folds, draw lines using a pencil and a scale.
You will notice different lines on the paper. Take any pair of lines and
observe their relationship with each other. Do they meet? If they do
not meet within the paper, do you think they would meet if they were
extended beyond the paper?

Fig. 5.1

In this chapter, we will explore the relationship between lines on a
plane surface. The table top, your piece of paper, the blackboard, and
the bulletin board are all examples of plane surfaces.
Let us observe a pair of lines that meet each other. You will notice
that they meet at a point. When a pair of lines meet each other at a
point on a plane surface, we say that the lines intersect each other.
Let us observe what happens when two lines intersect.
How many angles do they form?
In Fig. 5.2, where line l intersects line m, we can see that four angles
are formed.