Question

Решите уравнения за 8 класс

Answer 1

1.

$\frac{2}{7} {x}^{2} - 3x + 9 = 0 \: \: \: \: | \times 7 \\ 2 {x}^{2} - 21x + 63 = 0 \\ D = {( - 21)}^{2} - 4 \times 2 \times 63 = 441 - 504 = - 63$

Ответ: нет корней

2.

$\frac{1}{2} {x}^{2} - 3x + \frac{9}{2} = 0 \: \: \: \: | \times 2 \\ {x}^{2} - 6x + 9 = 0 \\ D = {( - 6)}^{2} - 4 \times 1 \times 9 = 36 - 36 = 0 \\ x = \frac{6}{2} = 3$

Ответ: x = 3

3.

${y}^{2} - y - 30 = 0 \\ D = {( - 1)}^{2} - 4 \times 1 \times ( - 30) = 1 + 120 = 121 \\ \sqrt{D} = \sqrt{121} = 11 \\ y_1 = \frac{1 + 11}{2} = \frac{12}{2} = 6 \\ y_2 = \frac{1 - 11}{2} = \frac{ - 10}{2} = - 5$

Ответ: y1 = 6; y2 = -5