f(x)=sin(x),求f(1+h),f(1+h)-f(1)/h

此即泰勒公式展开.
f(1+h)=f(1)+f'(1)h+1/2*f''(1)h^2+1/3!f'''(1)h^3+...
=sin(1)+cos(1)h-1/2sin(1)h^2-1/6cos(1)*h^3...
(f(1+h)-f(1))/h=cos(1)-1/2sin(1)*h-1/6*cos(1)*h^2+...
如果h足够小,取前面几项就可以满足精度的要求的啦。