Прочее

$$x_1 + x_2 = -7, \quad x_1\cdot x_2 = -8$$ $$x_1 = -8, \quad x_2 = 1$$

$$D = 16 - 4\cdot5\cdot(-1) = 36 \Rightarrow \sqrt{D} = 6$$ $$x _1 = \frac{4 + 6}{5\cdot2} = 1, \quad x_2 = \frac{4 - 6}{5\cdot2} = -0,2$$

$$x^2 - 3x - 10 = 0$$ $$D = 9 - 4\cdot1\cdot(-10) = 49 \Rightarrow \sqrt{D} = 7$$ $$x _1 = \frac{3 + 7}{1\cdot2} = 5, \quad x_2 = \frac{3 - 7}{1\cdot2} = -2$$

$$D = 25 - 4\cdot3\cdot2 = 1 \Rightarrow \sqrt{D} = 1$$ $$x _1 = \frac{5 + 1}{6} = 1, \quad x_2 = \frac{5 - 1}{6} = \frac{2}{3}$$

$$D = 16 - 4\cdot3\cdot(-20) = 256 \Rightarrow \sqrt{D} = 16$$ $$x _1 = \frac{4 + 16}{6} = \frac{10}{3}, \quad x_2 = \frac{4 - 16}{6} = -2$$