f(x)=x^2 .sin(1/x) ; x≠0=0 ; x=0lim(x->0) f(x)=lim(x->0) x^2.sin(1/x)=0=f(0)x=0 , f(x) 连续f'(0)=lim(h->0) [f(h)- f(0)] /h=lim(h->0) h.sin(1/h)=0