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计算:1/(x^2-7x+10)+1/(x^2-x-2)+1/(x^2+5x+4)+1/(x^2+11x+28)=( )

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计算:1/(x^2-7x+10)+1/(x^2-x-2)+1/(x^2+5x+4)+1/(x^2+11x+28)=( )
详写过程
1/(x^2-7x+10)+1/(x^2-x-2)+1/(x^2+5x+4)+1/(x^2+11x+28)
=[1/(x-5) -1/(x-2) + 1/(x-2) - 1/(x+1) + 1/(x+1)-1/(x+4) + 1/(x+4) - 1/(x+7)] /3
=[1/(x-5) -1/(x+7)] /3
再问: 为什么要除三
再答: 1/(x^2-7x+10) = [1/(x-5) -1/(x-2)]/3 其余依次类推