((а+2)/(а^2-a-6)-a/(a^2-6*a+9))*(2*a-6)^2=
=((a+2)/(a+2)(a-3) -a/(a-3)^2)*4(a-3)^2=
=(1/(a-3) -a/(a-3)^2)*4(a-3)^2=
=4(a-3)-4a=4a-12-4a=-12