$5x^2 - x - 1 = 0$
$D = 1^2 - 4 * 5 * (-1) = 1 + 20 = 21$
$x = \frac{1 ± \sqrt{21}}{10}$
$x_1 = \frac{1 - \sqrt{21}}{10} ≈ \frac{1 - 4,58}{10} = \frac{-3,58}{10} = -0,358 ≈ -0,36$
$x_2 = \frac{1 + \sqrt{21}}{10} ≈ \frac{1 + 4,58}{10} = \frac{5,58}{10} = 0,558 ≈ 0,56$
Ответ:
$x_1 ≈ -0,36$;
$x_2 ≈ 0,56$.

$2x^2 + 7x + 4 = 0$
$D = 7^2 - 4 * 2 * 4 = 49 - 32 = 17$
$x = \frac{-7 ± \sqrt{17}}{4}$
$x_1 = \frac{-7 - \sqrt{17}}{4} ≈ \frac{-7 - 4,12}{4} = \frac{-11,12}{4} = -2,78$
$x_2 = \frac{-7 + \sqrt{17}}{4} ≈ \frac{-7 + 4,12}{4} = \frac{-2,88}{4} = -0,72$
Ответ:
$x_1 ≈ -2,78$;
$x_2 ≈ -0,72$.

$3(y^2 - 2) - y = 0$
$3y^2 - 6 - y = 0$
$3y^2 - y - 6 = 0$
$D = 7^2 - 4 * 2 * 4 = 49 - 32 = 17$
$y = \frac{1 ± \sqrt{73}}{6}$
$y_1 = \frac{1 - \sqrt{73}}{6} ≈ \frac{1 - 8,54}{6} = \frac{-7,54}{6} ≈ -1,26$
$y_2 = \frac{1 + \sqrt{73}}{6} ≈ \frac{1 + 8,54}{6} = \frac{9,54}{6} = 1,59$
Ответ:
$y_1 ≈ -1,26$;
$y_2 ≈ 1,59$.

$y^2 + 8(y - 1) = 3$
$y^2 + 8y - 8 - 3 = 0$
$y^2 + 8y - 11 = 0$
$D = 4^2 - 1 * (-11) = 16 + 11 = 27$
$y = -4 ± \sqrt{27}$
$y_1 = -4 - \sqrt{27} ≈ -4 - 5,2 = -9,2$
$y_2 = -4 + \sqrt{27} ≈ -4 + 5,2 = 1,2$
Ответ:
$y_1 ≈ -9,2$;
$y_2 ≈ 1,2$.