已知f(x)连续,证明∫0xf(t)(x-t)dt=∫0x[∫0tf(u)du]dt.

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问题 已知f(x)连续,证明∫0xf(t)(x-t)dt=∫0x[∫0tf(u)du]dt.

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答案右边=∫0x[∫0tf(u)du]dt=[t∫0tf(u)du]|0x一∫0xtf(t)dt=x∫0xf(u)du-∫0xtf(t)dt=x∫0xf(t)dt一∫0xtf(t)dt=∫0xxf(t)dt-∫0xtf(t)dt=∫0x(x一t)f(t)dt=左边.

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