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 -

NextExitHome

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.

A

(Vertex) BC

arm

arm(Vertex) B

A

(Vertex) B

NextBackExitHome

There are five types of angles:-

1) Acute angle

2) Right angle

3) Obtuse angle

4) Straight angle

5) Reflex angle

TYPES OF ANGLES

ExitHome NextBack

Acute angle- An angle whose measure is more than 0 but less than 90 is called an

acute angle.

Given angle AOB measures 60 , which is less than 90 . So, it is an acute angle.

OO

A

B60

NextBackExitHome

Acute angle

Right angle-An angle whose measure is 90 is called a right angle.

Given angle POQ measures 90 . So, it is a right angle.

P

O Q

P

O Q

NextBackExitHome

Obtuse angle – An angle whose measure is more than 90 but less than 180 is called an obtuse angle.

Given angle PQR measures 120 , which is more

than 90 but less than 180 .

So, it is an obtuse angle.

P

QR

120

NextBackExitHome

Straight angle – An angle whose measure is 180 is called a straight angle.

Given angle BOD measures 180 .

So, it is a straight angle.

DB O D

180

NextBackExitHome

Reflex angle – An angle whose measure is more than

180 but less than 360 is called a reflex angle.

Given angle PQR measures 225 .

So, it is a reflex angle.

225225

P

Q R

NextBackExitHome Exit

Exercise

1) An angle whose measure is between 0 and 90 is called angle.

(a) acute (b) right

(c) obtuse

NextBack

ExitHome

2) An angle whose measure is 90 is called

angle.

(a) acute

(b) right

(c) obtuse

NextBackExitHome

3) An angle whose measure is more than 90 but

less than 180 is called angle.

(a) acute

(b) right

(c) obtuseNextBackExitHome

4) A reflex angle is always greater than

but less than 360 .

(a) 0

(b) 90

(c) 180

NextBackExitHome

5) Which of the following is an acute angle-

(a) 45

(b) 120

(c) 305

NextBackExitHome

6) What is the measure of straight angle-

(a) 90

(b) 180

(c) 360

NextBackExitHome

7) Which of the following is reflex angle-

(a) 150

(b) 60

(c) 320

BackExitHome ExitHome