设f(x2-1)=lnx2/(x2-2),且f[φ(x)]=lnx,求∫φ(x)dx.

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问题 设f(x2-1)=lnx2/(x2-2),且f[φ(x)]=lnx,求∫φ(x)dx.

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答案由f(x2-1)=lnx2/(x2-2)=ln[(x2-1)+1]/[(x2-1)-1],得f(x)=ln(x+1)/(x-1),再由f[φ(x))]=ln[φ(x)+1]/[φ(x)-1]=lnx,得φ(x)=(x+1)/(x-1),所以∫φ(x)dx=∫(x+1)/(x-1)dx=∫(1+2/x-1)dx=x+2ln|x-1|+C.

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