Question

Find the measure of the supplementary angle of $138^\circ $
(A) $48^\circ $
(B) $42^\circ $
(C) $52^\circ $
(D) $38^\circ $

Answer 1

Hint: Two angles are said to be complementary if their sum is equal to $90^\circ $ and two angles are supplementary, if their sum is equal to $180^\circ $.
For example two angles $30^\circ $ and $150^\circ $ are supplementary angles.

Complete step by step answer:
For supplementary angles, the sum of two angles is $180^\circ $
Let say x and y are supplementary angles, then $x + y = 180^\circ $
If $y = 138^\circ $
Then $x + 138^\circ = 180^\circ $
$x = 180^\circ - 138^\circ $
$x = 42^\circ $

So the correct answer is (B) $42^\circ $.

Note: General mistake done is we take sum of two angles as $90^\circ $ for supplementary angles also.