分母提出x=1/x^2/sqrt(1-1/x^2)dx令t=1/x，dt=-1/x^2dx原式=-dt/sqrt(1-t^2)
设 x = secu， 则 I = ∫secutanudu/(secutanu) = ∫du= u + C = arccos(1/x) + C = -arcsin(1/x) + C1
