cos(2 arctan(x)) =
- 1
- -x²
- x
- (1-x²)/(1+x²) (cos 2θ = cos²θ - sin²θ = (1-x²)/(1+x²))
Show answer and solution
Correct answer: D. (1-x²)/(1+x²) (cos 2θ = cos²θ - sin²θ = (1-x²)/(1+x²))
We have cos 2θ = 2 cos²θ - 1.
That is cos 2θ = 2/(1+x²) - 1.
So cos 2θ = (1-x²)/(1+x²).
Alternatively (1 - tan²θ)/(1+tan²θ).