∫√(x^2-1)/(x^2+1)Dx= ∫√(x^2-1)Darctanx
=√(x^2-1)arctanx- ∫2xarctanx/√(x^2-1)Dx
设x=tant
=√(x^2-1)arctanx- ∫t*2tant/sectDtant
后面就简单了