Question

If f(x) = cos²x + sec²x, then

A. f(x) < 1
B. f(x) = 1
C. 2 < f(x) < 1
D. f(x) ≥ 2

[Hint: A.M ≥ G.M.]

Answer 1

D. f(x) ≥ 2

Explanation:

According to the question,

We have, f(x) = cos²x + sec²x

We know that, A.M ≥ G.M.

⇒ cos0²x + sec²x ≥ 2

⇒ f(x) ≥ 2

Thus, option (D) f(x) ≥ 2 is the correct answer.