若f'(1)=3,则lim_(h->0)(f(1)-f(1-2h))/h= ( )
问题描述：
若f'(1)=3,则lim_(h->0)(f(1)-f(1-2h))/h= ( )
答
lim_(h->0)(f(1)-f(1-2h))/h
=lim_(h->0)2*(f(1)-f(1-2h))/2h
=2*lim_(h->0)(f(1)-f(1-2h))/2h
=2*f'(1)=2*3=6