(2a^4b^4/3-a^2b^4/9)/(-ab^3/3)^2
=a^2b^4(2a^2/3-1/9)/(a^2b^6/9)
=(2a^2/3-1/9)/(b^2/9)
=1/9*(6a^2-1)/(b^2/9)
=(6a^2-1)/b^2