设f(x)连续,则d2/dx2∫0x(x t)tf(x-t)dt=________.

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问题 设f(x)连续,则d2/dx20x(x t)tf(x-t)dt=________.

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答案f(x)

解析0xtf(x-t)dt→∫x0(x-u)f(u)(-du)=∫0x(x-u)f(u)du=x∫0xf(u)du-∫0xuf(u)du,于是d/dx∫0xtf(x-t)dt=∫0xf(u)du,故d2/dx20xtf(x-t)dt=f(x).
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