Question

Find cos 2x if sin x=1/2.

(a) 1/2

(b) 1/\(\sqrt{2}\)

(c) \(\sqrt{3}\)/2

(d) 1

The question was asked during an internship interview.

The query is from Trigonometric Functions of Sum and Difference of Two Angles-1 topic in division Trigonometric Functions of Mathematics – Class 11

Answer 1

Correct choice is (c) \(\sqrt{3}\)/2

The best explanation: We know, cos 2x = cos^2x – sin^2x = 1-2sin^2x {cos^2x = 1-sin^2x}

= 1-2(1/2)^2 = 1-2(1/4) = 1-1/2 = 1/2.