Which of the following is the best definition of a linear pair of angles?
1) A pair of supplementary angles is called a linear pair.
2) A pair of adjacent angles whose sum is equal to 180^°.

Solution:

This is true that the angles forming a linear pair sum up to 180^° but they need not be a pair of supplementary angle.

Linear pair angles are formed by two intersecting lines. The pair is adjacent and their sum is equal to 180^°.

Look at the figure shown below. ∠1 and ∠2 form a pair of linear angles.

i.e, ∠1 + ∠2 = 180^°

But every pair of supplementary angles can't be a linear pair. The angles 75° and 105° form a pair of supplementary angles but they do not form a linear pair because they are not adjacent.

Therefore, a pair of adjacent angles whose sum is equal to 180° represents a linear pair. Hence option 2) is correct.

Which of the following is the best definition of a linear pair of angles?

Summary:

Linear pair is defined as a pair of adjacent angles whose sum is equal to 180^°. Thus, Option 2) is correct.