来自林琦的问题
F(X)在X点处二阶可导,求LIM[F(X+H)-2F(X)+F(X-H)]/H^2H趋于0标答是F''(X)
F(X)在X点处二阶可导,求LIM[F(X+H)-2F(X)+F(X-H)]/H^2H趋于0
标答是F''(X)
1回答
2020-12-24 10:07
F(X)在X点处二阶可导,求LIM[F(X+H)-2F(X)+F(X-H)]/H^2H趋于0标答是F''(X)
F(X)在X点处二阶可导,求LIM[F(X+H)-2F(X)+F(X-H)]/H^2H趋于0
标答是F''(X)
以下极限都是h趋于0
lim[f(x+h)-2f(x)+f(x-h)]/h^2
(用洛必塔法则)
=lim[f'(x+h)-2f'(x)+f'(x-h)]/2h
=lim(1/2){[f'(x+h)-f'(x)]/h-[f'(x-h)-f'(x)]/(-h)}
=(1/2)[f''(x)-f''(x)]
=0
注意:
lim[f(x+h)-f(x)]/h=lim[f(x-h)-f(x)]/(-h)=f'(x)