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(e) Linear Pair of angles: When the sum of two adjacent angles is 180° C
they form a linear pair of angles. That means, a linear pair is a pair
of adjacent supplementary angles.
1
In the given figure, ∠ABC and ∠DBC are a linear pair. A B 2 D

Here, ∠1 + ∠2 = 180°.

Example 1: What would be the complement and supplement of a right angle?
Solution: Complement of a right angle = 90° – 90° = 0°

Supplement of a right angle = 180° – 90° = 90°.

Example 2: Can two acute angles be supplement? Justify your answer.
Solution: No. As an acute angle < 90°.

So, sum of two acute angles < 180°.

Thus, two acute angles can never be supplementary.
Answer the following questions:
1. Can two right angles be complementary?

2. Can two adjacent angles be complementary?
3. Can two obtuse angles be adjacent?

4. Can an acute angle be adjacent to an obtuse angle?
5. Can two right angles form a linear pair?

Practice Time 2F

1. On the dotted grid line, join the points using a pencil to make the following:
(a) Acute angle

(b) Obtuse angle

(c) Right angle
2. State whether the following statements are True (T) or False (F).

(a) The measure of an acute angle is less than 90°.

(b) The measure of an obtuse angle is equal to 90°.
(c) The measure of a reflex angle is > 180°.

(d) If ∠A = 45° and ∠B = 53°, then ∠A > ∠B.

(e) The measure of one complete angle is 180°.
3. Classify the following angles as acute, obtuse, right, straight, reflex or complete angles:

(a) 123° (b) 67° (c) 90° (d) 360°

(e) 213° (f) 116° (g) 180° (h) 88°

57 Lines and Angles