∵1/(x-7)+1/(x-8)=-1/(x-10)-1/(x-11)∴1/(x-7)+1/(x-8)+1/(x-10)+1/(x-11)=0∴（x-7+x-8+x-10+x-11）/(x-7)(x-8)(x-10)(x-11)=0∵分母不为0∴(x-7)(x-8)(x-10)(x-11)不=0∵ （x-7+x-8+x-10+x-11）/(x-7)(x-8)(x-10...