若函数f(x)在x=a处的导数为A,求lim(h→0)[f(a+h)-f(a+2h)]/h的值,

问题描述:

若函数f(x)在x=a处的导数为A,求lim(h→0)[f(a+h)-f(a+2h)]/h的值,

[f(a+h)-f(a+2h)]/h=[f(a+h)-fa+fa-f(a+2h)]/h=[f(a+h)-f(a)]/h+[f(a)-f(a+2h)]/h
=f'a-2*f'a
=-f'a也就是说【f(a+2h)-f(a)】/2h=A??