1/(x+5)+1/(x+8)=1/(x+6)+1/(x+7) (2x+13)/(x+5)(x+8)=(2x+13)/(x+6)(x+7) (2x+13)(1/(x+5)(x+8)-1/(x+6)(x+7))=0 (2x+13)(-2/(x+5)(x+8)(x+6)(x+7))=0 2x+13=0 x=-13/2