4) (2у - 1)(3у + 2) = 6y^2 + 4y - 3y - 2 = 6y^2 + y - 2;
5) (х^2 + у)(х + у^2) = x^3 + x^2y^2 + xy + y^3;
6)(х^2 + ху - у^2)(х + у) = x^3 + x^2y - xy^2 + x^2y + xy^2 - y^3 = x^3 + 2x^2y - y^3.
4) (2у - 1)(3у + 2) = 6y^2 + 4y - 3y - 2 = 6y^2 + y - 2;
5) (х^2 + у)(х + у^2) = x^3 + x^2y^2 + xy + y^3;
6)(х^2 + ху - у^2)(х + у) = x^3 + x^2y - xy^2 + x^2y + xy^2 - y^3 = x^3 + 2x^2y - y^3.