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\\November 23, 2023 10:09 AM Surender Prajapati Proof 5 Reader _________________________ Date: ___________________74

4. Name all the angles in the figures given below.
(a) (b)
A S
R
B T

O C P Q
5. Look at the given figure. Write: A
(a) the points lie on the angle. E
K
(b) the points lie in the interior of the angle. H I
(c) the points lie in the exterior of the angle. B D F G C

measurinG an anGle J

The measure of rotation between the arms of an angle gives the measure of the angle in

degrees (°). Observe the rotations of an arm of an angle.

B
B B

O A O A O A B O A

O O A O A O
A B A

B
B B

A complete turn of the arm about the vertex of the angle is divided into 360 equal parts.

Each part measures 1°. So, a complete turn about a point measures 360°.

The measurement of an angle is done by using a protractor.
a protractor

A protractor is a D-shaped instrument used for measuring the size of an angle.

It is semicircular in shape having two edges, one Inner
scale
semi-circular and the other a straight edge. The Outer
scale
semi-circular edge has two scales that are called the 60 70 80 90 100 70 120
110
90
80
50 120 110 100 60 130
inner and outer scales. Angles from 0° to 180° are Base 40 140 130 50 40 140
marked on both the scales. line 30 150 30 150
20 160 20 160
We read the outer scale clockwise and the inner scale 10 170 10 170
anticlockwise. The straight edge has a baseline. The 0 180 O 0 180 R

mid-point of the baseline is called its centre point. Centre

132 Mathematics-5