设f(x)连续,f(2)=0,且满足∫0xtf(3x—t)dt=arctan(1+ex),求∫23f(x)dx.

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问题 设f(x)连续,f(2)=0,且满足∫0xtf(3x—t)dt=arctan(1+ex),求∫23f(x)dx.

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答案0πtf(3x-t)dt[*]∫2x3xf(u)du =3x∫2x3xf(u)du—∫2x3xuf(u)du =arctan(1+ex). 两边求导得3∫2x3xf(u)du +3xf(3x) .3-3xf(2x) .2-9xf(3x)+4xf(2x)=[*]即3∫2x3xf(u)du-2xf(2x)=[*]令x=1,得∫23f(x)dx=[*].

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