设f(x)=ex-∫0x(x-t)f(t)dt,其中f(x)连续,求f(x).

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问题 设f(x)=ex-∫0x(x-t)f(t)dt,其中f(x)连续,求f(x).

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答案由f(x)=ex-∫0x(x-t)f(t)dt,得f(x)=ex-x∫0xf(t)dt+∫0xtf(t)dt,两边对x求导,得f’(x)=ex-∫0xf(t)dt,两边再对x求导得f"(x)+f(x)=ex,其通解为f(x)=C1cosx+C2sinax+1/2ex,在f(x)=e2-∫0x(x-t)f(t)dt中,令x=0得f(0)=1,在f’(x)=ex/sup>-∫0xf(t)dt中,令x=0得f’(0)=1,于是有C1=1/2,C2=1/2.故f(x)=1/2(cosx+sinx)+1/2ex

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