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为什么要除三1/（x^2-7x+10) = [1/(x-5) -1/(x-2)]/3其余依次类推