Page 172 - ICSE Math 6

Example 9: Construct an angle of magnitude 320°.
Solution: The angle of 320° is a reflex angle (more than 180°). So, construct an angle of
360° – 320° = 40°. Then draw the arc representing the angle on the outer side.

Draw a ray, say PQ, with initial point
P. P Q

70 80 90 100 70 120 130 R
110
60
80
50
Place the protractor on ray PQ such that 30 40 60 50 40 140 150
the mid-point of the protractor coincides 20 170 160 150 140 130 120 110 100 30 160
with point P and the base line coincides 10 20 170
with ray PQ. 0 180 P 10 0 180 Q

R
Mark a point, say R, on the division
which represents 40°.
Remove the protractor and draw a ray
joining the points P and R. Thus, ∠RPQ
is the required angle. P Q

EXERCISE 15.2

1. Measure the length of the line segment given below.

A B
2. Using a divider, compare the line segments given below.
B

C D
A

3. Verify the following by measuring the required line segments.
(a) PQ + QR = PR (b) PR – PQ = QR P Q R
4. Solve.

(a) 25° 18′ 50″ + 30° 50′ 45″ (b) 150° 22′ 33″ + 10° 50′ 55″
(c) 200° 22′ – 180° 15′ 20″ (d) 165° 35′ 45″ – 105° 55″

5. What is the magnitude of an angle which is 20° 30″ less than the sum of angles 72° 56′ 40″ and
180° 24′ 33″?

6. Measure the following angles using a protractor.

A A
A
(a) (b) (c)
B C
B B
C C

156