1) (4b^2+ 2a^2- 4ab)(3ab+2a^2-3b^2) = 12ab^3 + 6a^3b - 12a^2b^2 + 8a^2b^2+4a^4-8a^3b-12b^4+12ab^3 = 4a^4 - 12b^4 - 10a^2b^2 - 2a^3b +12ab^3
2) (5ab-3a^2-2b^2)(-4b^2-ab+6a^2) = -20ab^3+12a^2b^2+8b^4-5a^2b^2 +3a^3b+2ab^3+30a^3b-18a^4-12a^2b^2 = 8b^4-18a^4-5a^2b^2-18ab^3+33a^3b
3) (7+3a^2-3a)(5-2a-a^2) = 35+15a^2-15a-14a-6a^3+6a^2-7a^2+3a^4-3a^3= 3a^4-9a^3+14a^2-29a+35
4) (5xy^2-3x^3+2x^2y)(2x^2-xy-4y^2) =10x^3y^2-6x^5+4x^4y-5x^2y^3+3x^4y-2x^3y^2-20xy^4+12x^3y^2-8x^2y^3= 6x^5+7x^4y-20xy^4+20x^3y^2-13x^2y^3