The domain of f(x) = cos⁻¹(2x/1+x²) is:

The domain of f(x) = cos⁻¹(2x/1+x²) is:

• A. [−1, 1]
• B. R
• C. [−1/2, 1/2]
• D. [0, 1]

Answer: B) R

Explanation: cos⁻¹(y) requires y ∈ [−1, 1]. Here y = 2x/(1+x²). By AM-GM, |2x| ≤ 1+x² always, so |2x/(1+x²)| ≤ 1 for all real x. Domain is R.