lim（x→∞）((sin(1/x)*x√x)/(√x-1))
＝lim（x→∞）sin(1/x)*x
＝lim（x→∞）sin(1/x)/(1/x) (1/x=t)
=lim（t→0）sint/t
=1是第一步，看错啦lim（x→∞）√x/(√x-1))=1