503. 1) \((z^3-u^3)^2\); 2) \((m^3+n^3)^2\); 3) \((2m^3+3n)^2\).

1. \((z^3-u^3)^2=z^6-2z^3u^3+u^6\);
2. \((m^3+n^3)^2=m^6+2m^3n^3+n^6\);
3. \((2m^3+3n)^2=4m^6+12m^3n+9n^2\).

Ответ: \(z^6-2z^3u^3+u^6;\ m^6+2m^3n^3+n^6;\ 4m^6+12m^3n+9n^2\).