ln根号下(x+1)/(x-1)=ln根号下[1+2/(x-1)],x趋向于+∞时,2/(x-1)趋向于0,由等价无穷小得：ln根号下(x+1)/(x-1)=1/2ln[1+2/(x-1)]~1/(x-1) 则X趋向于+∞时,X*ln根号下(x+1)/(x-1)的极限=X*1/(x-1)的极限=1