Номер 3 и 5.Помогите!!!

3. 2
5.
(x + 4)(x - 3) = 2x^2 - 12 + 4x
x^2 -3x + 4x - 12 = 2x^2 + 4x - 12
x^2 + x - 12 = 2x^2 + 4x - 12
x^2 - 2x^2 + x - 4x = -12 + 12
-x^2 - 3x = 0
x^2 + 3x = 0
x(x + 3) = 0
x = 0 или x + 3 = 0 (x = -3)