$8x^2 - 14x + 5 = 0$
$D = 7^2 - 8 * 5 = 49 - 40 = 9$
$x = \frac{7 ± \sqrt{9}}{8}$
$x_1 = \frac{7 - 3}{8} = \frac{4}{8} = 0,5$
$x_2 = \frac{7 + 3}{8} = \frac{10}{8} = \frac{5}{4} = 1,25$
Ответ:
$x_1 = 0,5$;
$x_2 = 1,25$.

$12x^2 + 16x - 3 = 0$
$D = 8^2 - 12 * (-3) = 64 + 36 = 100$
$x = \frac{-8 ± \sqrt{100}}{12}$
$x_1 = \frac{-8 - 10}{12} = \frac{-18}{12} = -\frac{3}{2} = -1\frac{1}{2}$
$x_2 = \frac{-8 + 10}{12} = \frac{2}{12} = \frac{1}{6}$
Ответ:
$x_1 = -1\frac{1}{2}$;
$x_2 = \frac{1}{6}$.

$4x^2 + 4x + 1 = 0$
$D = 2^2 - 4 * 1 = 4 - 4 = 0$
$x = \frac{-2}{4} = -\frac{1}{2}$

$x^2 - 8x - 84 = 0$
$D = 4^2 - 1 * (-84) = 16 + 84 = 100$
$x = \frac{4 ± \sqrt{100}}{1}$
$x_1 = \frac{4 - 10}{1} = -6$
$x_2 = \frac{4 + 10}{1} = 14$
Ответ:
$x_1 = -6$;
$x_2 = 14$.

$x^2 + 6x - 19 = 0$
$D = 3^2 - 1 * (-19) = 9 + 19 = 28$
$x = \frac{-3 ± \sqrt{28}}{1} = -3 ± 2\sqrt{7}$

$5x^2 + 26x - 24 = 0$
$D = 13^2 - 5 * (-24) = 169 + 120 = 289$
$x = \frac{-13 ± \sqrt{289}}{5}$
$x_1 = \frac{-13 - 17}{5} = \frac{-30}{5} = -6$
$x_2 = \frac{-13 + 17}{5} = \frac{4}{5} = 0,8$
Ответ:
$x_1 = -6$;
$x_2 = 0,8$.

$x^2 - 34x + 289 = 0$
$D = 17^2 - 1 * 289 = 0$
x = 17

$3x^2 + 32x + 80 = 0$
$D = 16^2 - 3 * 80 = 256 - 240 = 16$
$x = \frac{-16 ± \sqrt{16}}{3}$
$x_1 = \frac{-16 - 4}{3} = \frac{-20}{3} = -6\frac{2}{3}$
$x_2 = \frac{-16 + 4}{3} = \frac{-12}{3} = -4$
Ответ:
$x_1 = -6\frac{2}{3}$;
$x_2 = -4$.