x→∞时,|sinx|≤1∴lim sinx / x =0lim x sin(2/x) =lim 2sin(2/x) / (2/x)=lim< 2/x →0> 2sin(2/x) / (2/x)= 2 【这里将2/x看作整体,用极限limsint /t =1】lim 2sinx /x = 0∴原式=2