(x − 3)(x + 7) − (x + 7)(x − 8) = 0
(x + 7)(x − 3 − x + 8) = 0
5(x + 7) = 0
x + 7 = 0
x = −7

(4x − 9)(x − 2) + (1 − x)(x − 2) = 0
(x − 2)(4x − 9 + 1 − x) = 0
(x − 2)(3x − 8) = 0
$x_1 - 2 = 0 : (3x - 8)$
$x_1 - 2 = 0$
$x_1 = 2$;
$3x_2 - 8 = 0 : (x - 2)$
$3x_2 - 8 = 0$
$3x_2 = 8$
$x_2 = \frac{8}{3}$
$x_2 = 2\frac{2}{3}$.

0,2x(x − 5) + 8(x − 5) = 0
(x − 5)(0,2x + 8) = 0
$x_1 - 5 = 0 : (0,2x + 8)$
$x_1 - 5 = 0$
$x_1 = 5$;
$0,2x_2 + 8 = 0 : (x - 5)$
$0,2x_2 + 8 = 0$
$0,2x_2 = -8$
$x_2 = -8 : 0,2$
$x_2 = -40$.

$7(x - 7) - (x - 7)^2 = 0$
(x − 7)(7 − x + 7) = 0
(x − 7)(14 − x) = 0
$x_1 - 7 = 0 : (14 - x)$
$x_1 - 7 = 0$
$x_1 = 7$;
$14 - x_2 = 0 : (x - 7)$
$14 - x_2 = 0$
$-x_2 = -14$
$x_2 = 14$.