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3. obtuse angle: An angle whose 4. Straight angle: An angle measuring

measure is more than 90° and less 180° is called a straight angle.
than 180° is called an obtuse angle. In the following figure, ∠ABC = 180°.
In the following figure, ∠ABC = 120°. 180°

A
A B C
Straight angle

120° Thus, ∠ABC is a straight angle.

B C
Obtuse angle
Thus, ∠ABC is an obtuse angle.

5. reflex angle: An angle greater than 6. Complete angle: An angle around
180° and less than 360° is called a a point is 360° and is called a
reflex angle. Here, ∠ROK = 250°. complete angle.

250° In the following figure, ∠XYZ = 360°.

O X
K
Reflex angle Y Z
Complete angle

Thus, it is a complete angle.
R

So, ∠ROK is a reflex angle.

Exercise 5C

1. Identify the types of angles.

a. b. c. d.

___________ ___________ ______________ ______________

112 Mathematics 5