1) (a + 3b)^2 - (3a - b)^2 = a^2 + 9b^2 + 6ab - 9a^2 - b^2 + 6ab = -8a^2 + 8b^2 + 12ab.
2) a - b^2 - 6 + a^2 = a - b^2 - 6.
3) 3 (2 - x)^2 - (2x^2 + x - 5) · (x^2 - 2) + (x^2 + 4) · (4 + x^2) = 3 · (4 + x^2 - 4x) - (2x^4 - 4x^2 + x^3 - 2x - 5x^2 + 10) + 4x^2 + x^4 + 16 + 4x^2 = 12 + 3x^2 - 12x - 2x^4 + 4x^2 - x^3 + 2x + 5x^2 - 10 + 4x^2 + x^4 + 16 + 4x^2 = 18 + 20x^2 - x^3 - x^4 - 10x.
Фух. Закончила...