$x^2 - 5 = (x + 5)(2x - 1)$
$x^2 - 5 = 2x^2 + 10x - x - 5$
$x^2 - 2x^2 - 10x + x = -5 + 5$
$-x^2 - 9x = 0$
x(−x − 9) = 0
x = 0 или −x − 9 = 0
−x = 9
x = −9
Ответ:
$x_1 = 0$;
$x_2 = -9$.

$2x - (x + 1)^2 = 3x^2 - 6$
$2x - (x^2 + 2x + 1) - 3x^2 + 6 = 0$
$2x - x^2 - 2x - 1 - 3x^2 + 6 = 0$
$-4x^2 + 5 = 0$
$-4x^2 = -5$
$x^2 = \frac{5}{4}$
$x = ±\sqrt{\frac{5}{4}}$
$x = ±\frac{\sqrt{5}}{2}$

$6a^2 - (a + 2)^2 = -4(a - 4)$
$6a^2 - (a^2 + 4a + 4) = -4a + 16$
$6a^2 - a^2 - 4a - 4 + 4a = 16$
$5a^2 = 16 + 4$
$5a^2 = 20$
$a^2 = 4$
a = ±2

(5y + 2)(y − 3) = −13(2 + y)
$5y^2 + 2y - 15y - 6 = -26 - 13y$
$5y^2 - 13y + 13y = -26 + 6$
$5y^2 = -20$
$y^2 = -4$
уравнение не имеет корней