Question

Find general solution to equation cos x = – 1/√2.

(a) x = 2nπ±7π/4

(b) x = 2nπ±3π/4

(c) x = 2nπ±π/4

(d) x = 2nπ±π/3

I have been asked this question in a job interview.

My query is from Trigonometric Equations topic in chapter Trigonometric Functions of Mathematics – Class 11

Answer 1

Correct option is (c) x = 2nπ±π/4

The best explanation: cos x = – 1/√2

cos x = – cos π/4 = cos (π- π/4) = cos 3π/4

So, x = 2nπ±π/4.