化简1/1+x+2/1+x^2+4/1+x^4+8/1+x^8+…+n/1+x^n-2n/1-x^2n

化简：a‹n›=1/(1+x)+2/(1+x^2)+4/(1+x^4)+8/(1+x^8)+…+n/(1+x^n)-2n/(1-x^2n)
2n/(1-x^2n)=2n/(1-xⁿ)(1+xⁿ)
当n=1时,a₁=1/(1+x)-2/(1-x)(1+x)=[1/(1+x)][1-2/(1-x)]=[1/(1+x)][-(1+x)/(1-x)]=-1/(1-x)
当n=2时,a₂=1/(1+x)+2/(1+x²)-4/(1-x²)(1+x²)=1/(1+x)+[2/(1+x²)][1-2/(1-x²)]
=1/(1+x)+[2/(1+x²)][-(1+x²)/(1-x²)]=1/(1+x)-2/(1-x²)=[1/(1+x)][1-2/(1-x)]
=[1/(1+x)][-(1+x)/(1-x)]=-1/(1-x)
当n=3时,a₃=1/(1+x)+2/(1+x²)+4/(1+x⁴)-8/(1-x⁴)(1+x⁴)
=1/(1+x)+2/(1+x²)+[4/(1+x⁴)][1-2/(1-x⁴)]=1/(1+x)+2/(1+x²)+[4/(1+x⁴)][-(1+x⁴)/(1-x⁴)]
=1/(1+x)+2/(1+x²)-4/(1-x⁴)=1/(1+x)+2/(1+x²)-4/(1+x²)(1-x²)=1/(1+x)+[2/(1+x²)][1-2/(1-x²)]
=1/(1+x)+[2/(1+x²)][-(1+x²)/(1-x²)]=1/(1+x)-2/(1-x²)=[1/(1+x)][1-2/(1-x)]=[1/(1+x)][-(1+x)/(1-x)]
=-1/(1-x)
.依此类推得：a‹n›=1/(1+x)+2/(1+x^2)+4/(1+x^4)+8/(1+x^8)+…+n/(1+x^n)-2n/(1-x^2n)=-1/(1-x).
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