Question

Решите уравнение по алгебре 8 класс способом подстановки, второй вариант​

Answer 1

$1) \\ 2x + y = 4 \\ x - y = 5 \\ \\ y = 4 - 2x \\ x - y = 5 \\ \\ x - (4 - 2x) = 5 \\ x - 4 + 2x = 5 \\ 3x = 9 \\ x = 3 \\ y = 4 - 6 \\ y = - 2$

Ответ:

х=3

у=-2

$2) \\ 3x + 4y = - 1 \\ 2x + 5y = 4 \\ \\ 6x + 8y = - 2 \\ 6x + 15y = 12 \\ \\ 6x = - 2 - 8y \\ 6x + 15y = 12 \\ \\ - 2 - 8y + 15y = 12 \\ 7y = 14 \\ y = 2 \\ 6 x = - 2 - 16 \\ x = - 3$

Ответ:

х=-3

у=2

$3) \\ xy = 32 \\ x + y = 12 \\ \\ x = 12 - y \\ xy = 32 \\ \\ 12y - {y}^{2} - 32 = 0 \\ \\ d = 144 - 128 = {4}^{2} \\ y1 = \frac{- 12 + 4}{ - 2} = 4 \\ y2 = \frac{ - 12 - 4}{ - 2} = 8 \\ \\ x1 = 8 \\ x2 = 4$

Ответ:

x1= 8

y1=4

x2=4

y2=8