Page 173 - ICSE Math 6

A A

(d) (e) (f) A O
B
B O O B
7. Construct the following angles using a protractor.
(a) 12° (b) 26° (c) 166° (d) 324° (e) 90°

AT A GLANCE

¾ Two rays having the same initial point form an angle.
¾ The area inside the arms of an angle is its interior and the area outside the arms is its exterior.
¾ Magnitude of an angle is the amount of rotation which one of the arms undergoes around the
vertex to coincide with the other arm.
¾ On the basis of magnitudes, different types of angles are:
(a) Acute angle; with magnitude more than 0° and less than 90°.
(b) Right angle; with magnitude 90°.
(c) Obtuse angle; with magnitude more than 90° and less than 180°.
(d) Straight angle; with magnitude 180°.
(e) Reflex angle; with magnitude more than 180° and less than 360°.
¾ Zero angle is an angle with magnitude 0° and complete angle is an angle with magnitude 360°

¾ Equal angles are called congruent angles and the angles formed by two intersecting lines without
any common arm are called vertically opposite angles.

¾ The sum of measures of complementary angles is 90° and the sum of measures of supplementary
angles is 180°.

¾ Two angles lying on the opposite sides of a common arm and having the same vertex are called
adjacent angles and two adjacent supplementary angles form a linear pair.

¾ A protactor is a geometrical instrument which is used for measuring and constructing angles.

MENTAL MATHS

1. Write True or False.

(a) An angle can be written in only one way.
(b) Interior and exterior of an angle extend endlessly.
(c) Magnitude of an obtuse angle is 90°.

(d) A complete angle is of magnitude 180°.
2. Fill in the blanks.
(a) The arms of an angle separate its interior and __________.
(b) 1° = __________′
(c) 1′ = __________″

(d) 1 complete angle = __________
(e) Angles opening on the right are measured using the __________ scale of a protractor and
angles opening on the left are measured using the __________ scale.

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