令根号下x-1=t,则x=t^2+1,t>0
d(x^2 arctan根号下X-1)=d((t^2+1)^2 arctant)=[2(t^2+1)*2t*arctant+t^2+1)^2*1/(t^2+1)]dt
=(t^2+1)*(1+4arctant)dt