证明:设函数f(x)在[一a,a]上连续,那么: (1)当f(x)为奇函数时,则∫-aaf(x)dx=0; (2)当f(x)为偶函数时,则∫-aaf(x)dx=2∫0af(x)dx.

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问题 证明:设函数f(x)在[一a,a]上连续,那么:
(1)当f(x)为奇函数时,则∫-aaf(x)dx=0;
(2)当f(x)为偶函数时,则∫-aaf(x)dx=2∫0af(x)dx.

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答案因为∫-a0f(x)dx[*]∫0af(一t)dt,所以: (1)当f(x)为奇函数时,有 ∫-aaf(x)dx=∫-a0f(x)dx+∫0af(x)dx=∫0af(一t)dt+∫0af(x)dx =-∫0af(t)dx+∫0af(x)dx=0. (2)当f(x)为偶函数时,有 ∫-aaf(x)dx=∫-a0f(x)dx+∫0af(x)dx =∫0af(-t)dt+∫0af(x)dx =∫0af(t)dt+∫0af(x)dx=2∫0af(x)dx. 证毕.

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