lim(h趋于0)[f(1+3h)-f(1)]/h=3,则
lim(h趋于0)3[f(1+3h)-f(1)]/3h=3,
即3lim(h趋于0)[f(1+3h)-f(1)]/3h=3
因为f'(1)=lim(h趋于0)[f(1+3h)-f(1)]/3h
所以3f'(1)=3lim(h趋于0)[f(1+3h)-f(1)]/3h=3
所以f'(1)=3/3=1
lim(h趋于0)[f(1+3h)-f(1)]/h=3,则
lim(h趋于0)3[f(1+3h)-f(1)]/3h=3,
即3lim(h趋于0)[f(1+3h)-f(1)]/3h=3
因为f'(1)=lim(h趋于0)[f(1+3h)-f(1)]/3h
所以3f'(1)=3lim(h趋于0)[f(1+3h)-f(1)]/3h=3
所以f'(1)=3/3=1