Page 74 - Maths Class 06

3. Ob tuse an gle:
An angle whose measure is greater than 90° and
less than 180° is an obtuse angle.

4. Straight an gle:
An angle whose measure is exactly 180° is a
straight angle.

5. Re flex an gle:
An angle whose measure is greater than 180°
and less than 360° is a reflex angle.

6. Com plete an gle:
An angle whose measure is exactly 360° is a
complete angle.Both the arms of complete
angle coincide (overlap each other)

EXAMPLE 1. Classify the fol low ing an gles as acute, ob tuse, re flex, right or straight an gle:
(a) 60° (b) 75° (c) 128° (d) 275°
SOLUTION : (a) and (b) are acute an gle.
(c) 128° is an obtuse angle (d) 275° is a reflex angle.
EX AM PLE 2. Find x in the given Fig. 5.1 D

SOLUTION : AOB is a straight an gle. \ Ð AOB = 180 °
Also, Ð AOB = ÐCOB + ÐCOD + Ð AOD
C
180° = 25° + 85° + x 85°
x = 180 ° - 110 ° x 25°
\ x = 70 ° A O B
Fig. 5.1

Exercise 5.2

1. Match the follow ing:
1
(a) 1 right angles (i) 285°
2
3
(b) more than th of revolution (ii) 180°
4
(c) half of the revolution (iii) 135°
1
(d) less than th of revolution (iv) 115°
4
1 1
(e) between th and of revolution (v) 52°
4 2
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