Index
 Introduction of angle
Types of angles
Exercise
Yesterday we have studied about the angles. Today, we will
study about the types of angles. Before continuing today's
class we will discuss little bit about the angle.
In mathematics, if two rays start from the same point,
the figure so formed is called an angle.
Examples -
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A
(Vertex) B
arm
C
Above fig. shows angle ABC.
The point where the rays intersect is called the vertex of
the angle. Here B is vertex. The two rays are called the
arms of the angle. Here BA and BC are arms of angle
ABC.
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TYPES OF ANGLES
There are five types of angles:1)
2)
3)
4)
5)
Acute angle
Right angle
Obtuse angle
Straight angle
Reflex angle
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Acute angle
Acute angle- An angle whose measure is
more than 0 but less than 90 is called an
acute angle.
A
60
B
O
Given angle AOB measures 60 , which is less than
90 .
So, it is an acute angle.
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Right angle-An angle whose measure is 90 is called a
right angle.
P
O
Q
Given angle POQ measures 90 .
So, it is a right angle.
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Obtuse angle – An angle whose measure is more than
90 but less than 180 is called an obtuse angle.
P
120
Q
R
Given angle PQR measures 120 , which is more
than 90 but less than 180 .
So, it is an obtuse angle.
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Straight angle – An angle whose measure is 180 is
called a straight angle.
180
B
O
D
Given angle BOD measures 180 .
So, it is a straight angle.
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Reflex angle – An angle whose measure is more than
180 but less than 360 is called a reflex angle.
225
Q
R
P
Given angle PQR measures 225 .
So, it is a reflex angle.
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Exercise
1) An angle whose measure is between 0 and 90
is called
angle.
(a) acute
(b) right
(c) obtuse
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2) An angle whose measure is 90 is called
angle.
(a) acute
(b) right
(c) obtuse
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3)
An angle whose measure is more than 90 but
less than 180 is called
angle.
(a) acute
(b) right
(c) obtuse
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4) A reflex angle is always greater than
but less than 360 .
(a) 0
(b) 90
(c) 180
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5) Which of the following is an acute angle-
(a) 45
(b) 120
(c) 305
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6) What is the measure of straight angle(a) 90
(b) 180
(c) 360
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7) Which of the following is reflex angle(a) 150
(b) 60
(c) 320
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