Page 99 - Revised Maths Wisdom Class - 6

Lines and Angles 97

2. Find the measure of the angle shown in each figure. (First estimate with your eyes and then find the actual
measure with a protractor).

(a) (b) (c) (d)

3. Find the angle measure between the hands of the clock in each figure.
(a) (b) (c)

9:00 a.m. 1:00 p.m. 6:00 p.m.

Types of Angles

We can classify the angles according to their degree measures.
Different Types of Angles

Name Definition Figure
P
An angle measuring more than 0° but less than 90° is called an
1. Acute angle Acute angle Q
acute angle. For example, 30°, 45° and 60° are all acute angles.

R

An angle measuring more than 90° but less than 180° is called Obtuse angle B
2. Obtuse angle an obtuse angle. For example, 135°, 120° and 175° are all obtuse
angles.
A O
Y
An angle measuring more than 180° but less than 360° is called X
3. Reflex angle a reflex angle. For example, 230°, 275° and 359° are all reflex Reflex angle
angles.
Z
If the terminal position of the ray OP coincides with the initial
4. Zero angle position OQ, without making any rotation then the angle formed O P Q
is 0°. Zero angle
L

An angle measuring exactly 90° is called a right angle. It is
5. Right angle
marked as ‘ ’ instead of a curve as shown in the figure. 90°
M N
Right angle
180°
6. Straight angle An angle measuring exactly 180° is called a straight angle. J K L
Straight angle
If the terminal ray OB makes one complete rotation and
7. Complete angle coincides with the initial ray OA, then the angle so formed is O A B
called complete angle. Its measure is 360°. Complete angle