$(2x - 3)(5x + 1) = 2x + \frac{2}{5}$
$10x^2 - 15x + 2x - 3 - 2x - 0,4 = 0$
$10x^2 - 15x - 3,4 = 0$
$D = 15^2 - 4 * 10 * (-3,4) = 225 + 136 = 361$
$x = \frac{15 ± \sqrt{361}}{20}$
$x_1 = \frac{15 - 19}{20} = \frac{-4}{20} = -0,2$
$x_2 = \frac{15 + 19}{20} = \frac{34}{20} = 1,7$
Ответ:
$x_1 = -0,2$;
$x_2 = 1,7$.

(3x − 1)(x + 3) = x(1 + 6x)
$3x^2 - x + 9x - 3 = x + 6x^2$
$3x^2 + 8x - x - 6x^2 - 3 = 0$
$-3x^2 + 7x - 3 = 0$ |*(−1)
$3x^2 - 7x + 3 = 0$
$D = 7^2 - 4 * 3 * 3 = 49 - 36 = 13$
$x = \frac{7 ± \sqrt{13}}{6}$

$(x - 1)(x + 1) = 2(5x - 10\frac{1}{2})$
$x^2 - x + x - 1 = 10x - 2 * \frac{21}{2}$
$x^2 - x + x - 1 = 10x - 21$
$x^2 - 10x - 1 + 21 = 0$
$x^2 - 10x + 20 = 0$
$x = 5 ± \sqrt{5}$

−x(x + 7) = (x − 2)(x + 2)
$-x^2 - 7x = x^2 - 2x + 2x - 4$
$-x^2 - 7x - x^2 + 4 = 0$
$-2x^2 - 7x + 4 = 0$ |*(−1)
$2x^2 + 7x - 4 = 0$
$D = 7^2 - 4 * 2 * (-4) = 49 + 32 = 81$
$x = \frac{-7 ± \sqrt{81}}{4}$
$x_1 = \frac{-7 - 9}{4} = \frac{-16}{4} = -4$
$x_2 = \frac{-7 + 9}{4} = \frac{2}{4} = 0,5$
Ответ:
$x_1 = -4$;
$x_2 = 0,5$.