[(3-a)/(2a-4)]/{a+2-[5/(a-2)]}
= [(3-a)/(2a-4)]/{a+2-5/(a-2)}
= [(3-a)/2]/[(a+2)(a-2) - 5]
= (3-a)/[2(a^2 -9)]
= (3-a)/[2(a+3)(a-3)]
= -1/[2(a+3)]