Помогите решить #5 °° . Даю 20 баллов!!!

$y = {x}^{2} + 8x \\$

тогда

$y(y - 6) = 280 \\ {y}^{2} - 6y - 280 = 0 \\ y1 + y2 = 6 \\ y1 \times y2 = - 280 \\ y 1= 20 \\ y2 = - 14$

${x}^{2} + 8x = 20 \\ {x}^{2} + 8x - 20 = 0 \\ x1 \times x2 = - 20 \\ x1 + x2 = - 8 \\ x1 = - 10 \\ x2 = 2$

${x}^{2} + 8x = - 14 \\ {x}^{2} + 8x + 14 = 0 \\ d = 64 - 4 \times 14 = 8 = 2 \sqrt{2} \\ x3 = \frac{ - 8 - 2 \sqrt{2} }{2} = - 4 - \sqrt{2} \\ x4 = - 4 + \sqrt{2}$