Tìm x biết 4x(x + 1) + (3 - 2x)(3 + 2x) = 15

Tìm x, biết:
$$\begin{gathered} 1) 4x(x + 1) + (3 - 2x\left)\right(3 + 2x) = 15 \\ 2) x^2 - 6x = 0 \\ 3) 2x^3 - 5x^2 - 12x = 0 \\ 4) (x + 1)(x + 2) - (x + 2)(x + 3) = 0 \end{gathered}$$