[(a-1/3)^2+(a+1/3)^2](2a^2+2/9)
=[a^2-2/3a+1/9+a^2+2/3a+1/9](2a^2+2/9)
=(2a^2+2/9)(2a^2+2/9)
=4a^4+8/9a^2+4/81