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A line can be denoted by the letters such as l, m, n, …. Or if we take two points on the line as A and
B, it can be named as line AB or line BA and denoted by AB or BA .
A line has some properties.
• Only one line can be drawn through 2 points. A B
• A line has infinitely many points on it.
• Infinite lines can be drawn through a given point.
Line Segment Quick Check
If we cut a portion of a line, it is called a line segment. It has two Look around you and
endpoints. A line segment shows shortest distance between two points. list any 10 objects/
B C things that represents
lines or line segments.
A D
If A and B are two end points of a line segment, then it can be named as line segment AB or line
segment BA and it is denoted by AB or BA .
Ray
Ray is another part of a line. It is a combination of a line and a line segment that has one infinitely
extending end and one terminating end. A ray is represented by AB . A B
Angle
When two rays or line segments originate from a common end point or meet A
at a point, they form an angle. These two rays or the line segments are called
the arms of the angles and the common endpoint is called the vertex of the Arm
angle. An Angle is denoted by the symbol ‘∠’.
O Angle
In the adjacent figure, ∠AOB is an angle whose arms are OA and OB and O is Vertex Arm B
the vertex of the angle.
It can be denoted by ∠AOB or ∠BOA or ∠O. Symbol ‘∠’ stands for angle. We can also represent an
angle by numbers ∠1, ∠2 , ∠3,… or by using alphabets as ∠x, ∠y, ∠a , ∠b, …
The inclination between the arms shows the magnitude of the angle.
Types of Angles
The classification of angles is based on the measure of the angles. Based on this there are various
types of angles.
Acute angle: An angle which is more than 0° and less than 90° is A
called an acute angle. For example, 40°, 60°, 85°, etc.
60°
O B
Right angle: An angle equal to 90° is called a right angle. A
90°
O
B
149 Lines and Angles
