(6-y)(6+y)/(y-8)(y/(y-6)-2y/(y-6)^2)+12y/(y-6)=
=(6-y)(6+y)/(y+8)*(y^2-8y)/(y-6)^2+(12-y)/(y-6)=
=-y(6+y)/(y-6)+12y/(y-6)=(-6y-y^2+12y)/(y-6)=(6y-y^2)/(y-6)=y(6-y)/(y-6)=-y
