Which substitution is most effective for evaluating ∫1xx2−1dx\int \frac{1}{x\sqrt{x^2-1}} dx∫xx2−11dx?
u=x2−1u = x^2-1u=x2−1
x=sec(θ)x = \sec(\theta)x=sec(θ)
u=x2−1u = \sqrt{x^2-1}u=x2−1
x=sin(θ)x = \sin(\theta)x=sin(θ)