Answer:
4m^4 - 8/3m^2 n^2 + 4/9n^4
Step-by-step explanation:
(2m^2 - 2/3n^2)(2m^2 - 2/3n^2)
= 2m^2(2m^2 - 2/3n^2) - 2/3n^2(2m^2 - 2/3n^2)
= 4m^4 - 4/3m^2 n^2 - 4/3m^2n^2 + 4/9n^4
= 4m^4 - 8/3m^2 n^2 + 4/9n^4
