首先乘法求导然后是复合函数求导。x^2sin(1/x)=2xsin(1/x)+x^2cos(1/x)(1/x)'=2xsin(1/x)-cos(1/x)
等于2xsin?1/x?-x2cos?1/x?×xˉ2=2xsin?1/x?-cos?1/x?
