求证:2/x2-1+4/x2-4+6/x2-9+…+20/x2-100=11/(x-1)(x+10)+…+11/(x-1

1个回答

  • 先证明了左右两边首尾两项的等量关系:

    2/(x^2-1)+20/(x^2-100)=(22x^-220)/[(x^2-1)(x^2-100)]

    =(22x^-220)/[(x+1)(x-1)(x+10)(x-10)]

    =22(x^-10)/[(x+1)(x-1)(x+10)(x-10)]

    11/(x-1)(x+10)+11/(x-10)(x+1)=11(2x^2+20)/[(x+1)(x-1)(x+10)(x-10)]

    =22(x^2+10)/[(x+1)(x-1)(x+10)(x-10)]

    即2/(x^2-1)+20/(x^2-100)=11/(x-1)(x+10)+11/(x-10)(x+1)

    同理4/(x^2-4)+18/(x^2-81)=11/(x-2)(x+9)+11/(x-9)(x+2)

    ……

    所以:2/(x2-1)+4/(x2-4)+6/(x2-9)+…+20/(x2-100)=11/(x-1)(x+10)+…+11/(x-10)(x+1)