鸡之与鸡
t=x2,所以t-->0+,这一步就是用了洛必达法则,上下同时求导根据泰勒公式f(x+h)=f(x)+f'(x)h+(1/2)f''(x)h^2+o(h^2)于是:f(x)+hf'(x+θh)=f(x)+f'(x)h+(1/2)f''(x)h^2+o(h^2)θ{[f'(x+θh)-f'(x)]/θh}=(1/2)f''(x)+o(h^2)/h^2lim(h→0)θ{[f'(x+θh)-f'(x)]/θh}=lim(h→0)[(1/2)f''(x)+o(h^2)/h^2]lim(h→0)θf''(x)=(1/2)f''(x)lim(h→0)θ=1/2本回答被网友采纳