f ' (0) = Limit [ ( f(x)-f(0) ) / (x-0) , x->0 ] = Limit [ x^2 sin(1/x) / x , x->0 ] = Limit [ x sin(1/x) , x->0 ] = 0选 D 注:sin(1/x) 有界,无穷小与有界函数的乘积仍是无穷小, Limit [ x sin(1/x) , x->0 ] = 0