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\ 19-Nov-2025 Bharat Arora Proof-9 Reader’s Sign _______________________ Date __________

Angle

• Two rays having a common endpoint form an angle . B
• The two rays forming an angle are called the arms of

the angle. The common endpoint is called the vertex
vertex arms
of the angle.
The symbol of an angle is ∠.
O A
naming an Angle

To name an angle, we first take a point on one arm (ray), then the vertex and then a
point on the other arm (ray).

In the figure above, the rays OA and OB form an angle at O, which is denoted by
∠AOB or ∠BOA. Here, OA and OB are the arms and O is the vertex of this angle.

Interior and exterior of an Angle

Consider an angle, say ∠AOB as shown in the adjoining figure.
B
Take a point P on ray OA and a point R on ray OB. R
We say that the points P and R lie on ∠AOB.
S
Mark two points M and N inside ∠AOB, and two points S M
and T outside ∠AOB. We say that M and N lie on the interior N

of ∠AOB and S and T lie on the exterior of ∠AOB.
O P A
The shaded region denotes the interior of ∠AOB. T

Exercise 5A

1. Which of the following figures shows an angle?

a. b. c. d.

2. name the following angles:

a. P b. X Z c. M d. E

N
L
F G
Q R
Y

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Geometry