$x^2 - x - 12 = 0$
$D = b^2 - 4ac = (-1)^2 - 4 * 1 * (-12) = 1 + 48 = 49 > 0$
$x_1 = \frac{-b + \sqrt{D}}{2a} = \frac{1 + \sqrt{49}}{2 * 1} = \frac{1 + 7}{2} = \frac{8}{2} = 4$
$x_2 = \frac{-b - \sqrt{D}}{2a} = \frac{1 - \sqrt{49}}{2 * 1} = \frac{1 - 7}{2} = \frac{-6}{2} = -3$
Ответ: −3; 4.

$x^2 + 2x - 35 = 0$
$D = b^2 - 4ac = 2^2 - 4 * 1 * (-35) = 4 + 140 = 144 > 0$
$x_1 = \frac{-b + \sqrt{D}}{2a} = \frac{-2 + \sqrt{144}}{2 * 1} = \frac{-2 + 12}{2} = \frac{10}{2} = 5$
$x_2 = \frac{-b - \sqrt{D}}{2a} = \frac{-2 - \sqrt{144}}{2 * 1} = \frac{-2 - 12}{2} = \frac{-14}{2} = -7$
Ответ: −7; 5.

$3x^2 - 16x + 5 = 0$
$D = b^2 - 4ac = (-16)^2 - 4 * 3 * 5 = 256 - 60 = 196 > 0$
$x_1 = \frac{-b + \sqrt{D}}{2a} = \frac{16 + \sqrt{196}}{2 * 3} = \frac{16 + 14}{6} = \frac{30}{6} = 5$
$x_2 = \frac{-b - \sqrt{D}}{2a} = \frac{16 - \sqrt{196}}{2 * 3} = \frac{16 - 14}{6} = \frac{2}{6} = \frac{1}{3}$
Ответ: $\frac{1}{3}; 5$.

$16x^2 - 24x + 3 = 0$
$D = b^2 - 4ac = (-24)^2 - 4 * 16 * 3 = 576 - 192 = 384 > 0$
$x_1 = \frac{-b + \sqrt{D}}{2a} = \frac{24 + \sqrt{384}}{2 * 16} = \frac{24 + \sqrt{64 * 6}}{32} = \frac{24 + 8\sqrt{6}}{32} = \frac{8(3 + \sqrt{6})}{32} = \frac{3 + \sqrt{6}}{4}$
$x_2 = \frac{-b - \sqrt{D}}{2a} = \frac{24 - \sqrt{384}}{2 * 16} = \frac{24 - \sqrt{64 * 6}}{32} = \frac{24 - 8\sqrt{6}}{32} = \frac{8(3 - \sqrt{6})}{32} = \frac{3 - \sqrt{6}}{4}$
Ответ: $\frac{3 - \sqrt{6}}{4}; \frac{3 + \sqrt{6}}{4}$.

$4x^2 + 28x + 49 = 0$
$D = b^2 - 4ac = 28^2 - 4 * 4 * 49 = 784 - 784 = 0$
$x = \frac{-b + \sqrt{D}}{2a} = \frac{-28 + \sqrt{0}}{2 * 4} = \frac{-28}{2 * 4} = \frac{-7}{2} = -3,5$
Ответ: −3,5

$3x^2 + 21x - 90 = 0$
$D = b^2 - 4ac = 21^2 - 4 * 3 * (-90) = 441 + 1080 = 1521 > 0$
$x_1 = \frac{-b + \sqrt{D}}{2a} = \frac{-21 + \sqrt{1521}}{2 * 3} = \frac{-21 + 39}{6} = \frac{18}{6} = 3$
$x_2 = \frac{-b - \sqrt{D}}{2a} = \frac{-21 - \sqrt{1521}}{2 * 3} = \frac{-21 - 39}{6} = \frac{-60}{6} = -10$
Ответ: −10; 3.