令 x = tant, dx = sec²t dt, sqrt(x^2+1) = sect
I = ∫ sect / tan²t dt = ∫ cost /sin²t dt = -1/ sint + C
= - sqrt(x^2+1) / x + C
令 x = tant, dx = sec²t dt, sqrt(x^2+1) = sect
I = ∫ sect / tan²t dt = ∫ cost /sin²t dt = -1/ sint + C
= - sqrt(x^2+1) / x + C