$2x^2 - 5x + b = 2(x - 3)(x - x_2)$
$x_1 = 3$
$x_1 + x_2 = -\frac{b}{a} = -\frac{-5}{2} = 2,5$
$3 + x_2 = 2,5$
$x_2 = 2,5 - 3$
$x_2 = -0,5$
$x_1x_2 = \frac{c}{a} = \frac{b}{a} = \frac{b}{2}$
$\frac{b}{2} = 3 * (-0,5)$
$\frac{b}{2} = -1,5$
b = −1,5 * 2
b = −3
Ответ: при b = −3

$-4x^2 + bx + 2 = -4(x + 1)(x - x_2)$
$x_1 = -1$
$x_1x_2 = \frac{c}{a} = \frac{2}{-4} = -0,5$
$-1 * x_2 = -0,5$
$x_2 = 0,5$
$x_1 + x_2 = -\frac{b}{a} = -\frac{b}{-4} = \frac{b}{4}$
$\frac{b}{4} = -1 + 0,5$
$\frac{b}{4} = -0,5$
b = −0,5 * 4
b = −2
Ответ: при b = −2

$3x^2 - 4x + b = 3(x - x_1)(x - x_2)$
$3x - 3x_1 = 3x - 2$
$3x - 3x_1 - 3x = -2$
$-3x_1 = -2$
$x_1 = \frac{2}{3}$
$x_1 + x_2 = -\frac{b}{a} = -\frac{-4}{3} = \frac{4}{3}$
$\frac{2}{3} + x_2 = \frac{4}{3}$
$x_2 = \frac{4}{3} - \frac{2}{3}$
$x_2 = \frac{2}{3}$
$x_1x_2 = \frac{c}{a} = \frac{b}{3}$
$\frac{b}{3} = \frac{2}{3} * \frac{2}{3}$
$\frac{b}{3} = \frac{4}{9}$ |* 9
3b = 4
$b = \frac{4}{3} = 1\frac{1}{3}$
Ответ: при $b = 1\frac{1}{3}$