1/(x-6)+1/(x-11)=1/(x-7)+1/(x-12)(x-11)(x-7)(x-12)+(x-6)(x-7)(x-12)=(x-6)(x-11)(x-12)+(x-6)(x-11)(x-7)(x-11+x-6)(x-7)(x-12)=(x-6)(x-11)(x-12+x-7)(2x-17)(x-7)(x-12)=(x-6)(x-11)(2x-19)(2x-17)(x^2-19x+84...