8(a^2 + 2b^2)
that's about all you can factor, if you want rational coefficients
otherwise you might do this
8(a+sqr2bi)(a-sqr2bi) but that's irrational coefficents plus imaginary factors
still it might impress some math instructors. a^2-b^2 factors into (a+b)(a-b)
a^2 + b^2 doesn't really factor in the normal sense.