Page 153 - Math Skill - 5

Geometry 151

Step 2: Starting from 0° of the inner scale, move towards C

point C and note the mark on the rim of the

protractor where ray BC passes.

Step 3: Read the mark carefully taking care of smaller
divisions also.

Thus, ∠ABC = 65° B A

Types of Angles

Based on their measures, angles are classified as follows: 12
R 1
Acute Angle
An angle whose measure is more than 0° and less than 9 3
90° is called an acute angle. In the figure, ∠PQR = 50°, 50° Q
which is an acute angle.
P
12 6
Y
Right Angle
An angle whose measure is 90°, is called a right
9 3
90° angle. In the figure, ∠XOY = 90°, which is a right
angle. A right angle is denoted as ‘ ’ or ‘ ’.
O
X 6 11 12

Obtuse Angle T

An angle whose measure is more than 90° and 9 3
less than 180° is called an obtuse angle. In the 120°
figure, ∠PST = 120°, which is an obtuse angle. P S 6
12

Straight Angle
180°
9 3 An angle whose measure is 180° is called a
L O M straight angle. In the figure, ∠LOM = 180°, which
is a straight angle.
6 12
Reflex Angle 250°

An angle whose measure is more than 180° and less than I H
360° is called a reflex angle. In the figure, ∠GHI = 250° 9 3
which is a reflex angle.
12 Complete Angle G 6 5

360° An angle of measure 360° is called a complete angle.
9 3 In the figure, ∠BAC = 360° which is a complete angle.
C B A
Note that the ray AB rotates completely to overlap on
6
ray AC .