1) (a - 4b)(a + 4b) = a^2 - 16b^2;
2) 5a(a + 3) - (a - 3)^2 = 5a * a + 5a * 3 - a^2 + 6a - 9 = 5a^2 + 15a - a^2 + 6a - 9 = 4a^2 + 21a - 9.
1) (a - 4b)(a + 4b) = a^2 - 16b^2;
2) 5a(a + 3) - (a - 3)^2 = 5a * a + 5a * 3 - a^2 + 6a - 9 = 5a^2 + 15a - a^2 + 6a - 9 = 4a^2 + 21a - 9.