5) (2x-1)(2x+1) = 2(x-3)² + x(2x-8).

Решение:
$$4x^2 - 1 = 2(x^2 - 6x + 9) + 2x^2 - 8x$$
$$4x^2 - 1 = 2x^2 - 12x + 18 + 2x^2 - 8x$$
$$4x^2 - 1 = 4x^2 - 20x + 18$$
$$-1 = -20x + 18$$
$$20x = 19$$
$$x = \frac{19}{20}$$
Ответ: 19/20.