19) $$(6-x^2y^2)^2 = 6^2 - 2 \cdot 6 \cdot x^2y^2 + (x^2y^2)^2 = 36 - 12x^2y^2 + x^4y^4$$
Ответ: $$36 - 12x^2y^2 + x^4y^4$$