∫ sqrt(1 x^2)/x dx令 x = tan(u) 则 dx = sec^2(u) du.sqrt(x^2 1) = sqrt(tan^2(u) 1) = sec(u) ,u = tan^(-1)(x):= ∫ csc(u) sec^2(u) du= ∫ (tan^2(u) 1) csc(u) du= ∫ (csc(u) tan(u) sec(u)) du= ∫ csc(u...∫ (csc(u) tan(u) sec(u)) du这个没看懂