f(x)在x→无穷大时极限为A,f(x)在R上连续,求证f(x)有界
limf(x)在x→无穷大时极限为A,且f(x)在R上连续,求证f(x)有界.
人气:465 ℃ 时间:2020-05-19 05:58:34
解答
对于ε=1,由lim(x→∞)f(x)=A,存在正数X,当|x|>X时,|f(x)-A|<1,所以|f(x)|<1+|A|.
f(x)在[-X,X]上连续,从而有界,所以存在正数M1,使得|f(x)|≤M1对任意的x∈[-X,X]恒成立.
取M=max{1+|A|,M1},则|f(x)|<M在R上恒成立,所以f(x)有界
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