(3x − 2)(3x + 2) − (2x − 5)(8x − 3) = 4x − 19
$9x^2 - 6x + 6x - 4 - (16x^2 - 40x - 6x + 15) = 4x - 19$
$9x^2 - 6x + 6x - 4 - 16x^2 + 40x + 6x - 15 - 4x = -19$
$-7x^2 + 42x = -19 + 4 + 15$
$-7x(x - 6) = 0$
$-7x_1 = 0 : (x - 6)$
$-7x_1 = 0$
$x_1 = 0$;
$x - 6 = 0 : (-7x)$
$x - 6 = 0$
$x_2 = 6$.

$\frac{1}{3}(12 + x^3) = \frac{1}{9}x^2 + 4$
$4 + \frac{1}{3}x^3 = (\frac{1}{3})^2x^2 + 4$
$\frac{1}{3}x^3 - (\frac{1}{3})^2x^2 = 4 - 4$
$\frac{1}{3}x^2(x - \frac{1}{3}) = 0$
$\frac{1}{3}x^2 = 0 : (x - \frac{1}{3})$
$\frac{1}{3}x^2 = 0$
$x^2 = 0$
$x_1 = 0$;
$x_2 - \frac{1}{3} = 0 : \frac{1}{3}x^2$
$x_2 - \frac{1}{3} = 0$
$x_2 = \frac{1}{3}$.