ПОМОГИТЕ ПОЖАЛУЙСТА

1)
$x + y = 7 \\ xy = 12 \\ \\ y = 7 - x \\ x(7 - x) = 12 \\ \\ y = 7 - x \\ 7x - {x}^{2} = 12 \\ \\ y = 7 - x \\ {x}^{2} - 7x + 12 = 0 \\ x1 = 4 \\ x2 = 3 \\ y1 = 3 \\ y2 = 4$
(x + y) = 7
Ответ: 7.

2)
${y}^{2} + {x}^{2} = 17 \\ y - 3x - 1 = 0 \\ \\ y = 3x + 1 \\ (3x + 1) ^{2} + {x}^{2} = 17 \\ \\ y = 3x + 1 \\ 9 {x}^{2} + 6x + 1 + {x}^{2} = 17 \\ \\ y = 3x + 1 \\ 10 {x}^{2} + 6x - 16 = 0 \\ \\ y = 3x + 1 \\ 5 {x}^{2} + 3x - 8 = 0 \\ d = {b}^{2} - 4ac = 9 - 4 \times 5 \times ( - 8) = 169 \\ x1 = \frac{ - 3 + 13}{10} = 1 \\ x2 = \frac{ - 3 - 13}{10} = - \frac{8}{5} \\ y1 = 4 \\ y2 = 3 \times ( - \frac{8}{5} ) + 1 = - \frac{24}{5} + \frac{5}{5} = - \frac{19}{5} \\ x1 + y1 = 5 \\ x2 + y2 = - \frac{27}{5}$
Ответ: 5.

3)
$x - y = 4 \\ xy = 5 \\ \\ x = 4 + y \\ y(4 + y) = 5 \\ \\ x = 4 + y \\ {y}^{2} + 4y - 5 = 0 \\ \\ x = 4 + y \\ y1 = - 5 \\ y2 = 1 \\ x1 = - 1 \\ x2 = 5 \\ x1 + y1 = - 6 \\ x2 + y2 = 6$
Ответ: 6.

4)
${x}^{2} + {y}^{2} = 10 \\ x - y = 2 \\ \\ x = 2 + y \\ {(2 + y)}^{2} + {y}^{2} = 10 \\ \\ x = 2 + y \\ 4 + 4y + {y}^{2} + {y}^{2} = 10 \\ \\ x = 2 + y \\ 2 {y}^{2} + 4y - 6 = 0 \\ \\ x = 2 + y \\ {y}^{2} + 2y - 3 = 0 \\ \\ x = 2 + y \\ y1 = - 3 \\ y2 = 1 \\ x1 = - 1 \\ x2 = 3 \\ x1 + y1 = - 4 \\ x2 + y2 = 4$
Ответ: 4.