12) $$-2ab^2+3a^2b+a^2 - (b^2 + 5a^2b-2ab^2) = -2ab^2 + 3a^2b + a^2 - b^2 - 5a^2b + 2ab^2$$
$$ -2ab^2 + 3a^2b + a^2 - b^2 - 5a^2b + 2ab^2 = -2a^2b + a^2 - b^2$$
Ответ: $$-2a^2b + a^2 - b^2$$