Which substitution is the most effective to evaluate ∫1xx2+1dx\int \frac{1}{x\sqrt{x^2+1}} dx∫xx2+11dx?
u=x2+1u = x^2+1u=x2+1
x=tan(θ)x = \tan(\theta)x=tan(θ)
u=1/xu = 1/xu=1/x
u=x2+1u = \sqrt{x^2+1}u=x2+1