Раскроем скобки и упростим уравнение:
$$(4x^2 - 4x + 1) - (x^2 - 9) = 4x + 6$$
$$4x^2 - 4x + 1 - x^2 + 9 = 4x + 6$$
$$3x^2 - 4x + 10 = 4x + 6$$
$$3x^2 - 8x + 4 = 0$$
$$D = b^2 - 4ac = (-8)^2 - 4 * 3 * 4 = 64 - 48 = 16$$
$$x_{1,2} = \frac{-b \pm \sqrt{D}}{2a} = \frac{8 \pm \sqrt{16}}{2 * 3} = \frac{8 \pm 4}{6}$$
$$x_1 = \frac{8 + 4}{6} = \frac{12}{6} = 2$$
$$x_2 = \frac{8 - 4}{6} = \frac{4}{6} = \frac{2}{3}$$
Ответ: $$x_1 = 2$$, $$x_2 = \frac{2}{3}$$