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The shortest path from A to B is called the line segment AB. Also, look at the two lines AB and CD shown here. B
It is denoted by AB. We may also call it the line segment BA and A B If we extend them towards the left, we find that they meet at A
denote it by BA. point O. C D
A B
The points A and B are called the end points of line segment AB. We can say that the lines AB and CD intersect at the point O. B
A line segment has a definite length, which can be measured. A B Hence, AB and CD are intersecting lines. A

parallel lines O C D
Think Tank Logical Thinking
When you have travelled by train, have you noticed the railway track?
Identify which of the following is an example of a point, a line segment or a plane:
1. Tip of a sharpened pencil 2. The edge of a book 3. Floor of a room It looks like two straight lines which never meet at any point and
extend endlessly. It is an example of parallel lines.
ray Thus, the lines which lie on the same plane and never intersect

If a line segment goes on endlessly in one direction, it is called A B are called parallel lines. Railway Track

a ray. The figure alongside represents a ray AB. FACTS Look at the two lines PQ and RS shown alongside. P Q
It is denoted by AB . The AB has one end point, namely A. The Š An infinite number of If we extend these lines on both sides, we find that they do R S
end point A is called the initial point of ray AB . lines can be drawn not intersect, even when we extend them to any extent.
through a point. Such lines are called parallel lines. FACTS
line Š Only a line segment can
be drawn through two Two parallel lines are indicated by identical standing Š Parallel lines are always the same
distance apart.
If a line segment is extended endlessly in both directions, it is given points. lines ‘| |’. Š Parallel lines lying on the same plane
called a line. perpendicular lines never intersect each other.

The figure alongside represents a line AB. It is denoted by AB or BA .
A B Look at the given pictures. In figures (i) and (ii),
A line may be represented by a small letter such as l, m, n, etc. l the objects make a right angle with the ground

A line has no end points. So, it does not have a definite length. and in figure (iii) the edges of the door meet at a
corner making a right angle.
Knowledge Desk Thus, two lines which intersect each other
making a right angle at the point of intersection
The shortest distance between two points is a straight line, which is known as the Euclidean Fig. (i) Fig. (ii) Fig. (iii)
distance. It is named after Euclid, a Greek mathematican, often called the ‘Father of are called perpendicular lines.
Geometry’. In the adjoining figure, lines f and g are perpendicular to each other. f
A Right
The symbol ‘ ’ is used for perpendicular and is read as is angle
intersecting lines perpendicular to. g
C O D
You have often seen a chauraha when you go to the market or We write it as f g or g f. B
school. A chauraha is a place where two roads cross or intersect f ⊥ g or AB ⊥ CD or OA ⊥ CD or OB ⊥ CD
each other at a point.

If two lines meet at a point or tend to meet if extended, they Think Tank Logical Thinking
are called intersecting lines. l Look at your surroundings and list some objects that represent:
Here, in the adjacent figure, lines l and m are intersecting lines 1. Intersecting lines. 2. Parallel lines. 3. Perpendicular lines.
intersecting at point O. O m Teacher’s Explain to the children that two straight lines intersect at one and only one point. Also, tell them that two lines

Tip are coinciding if they have all points in common.

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