Verified answer

Ответ:

(-23; 6)

Пошаговое объяснение:

{х + 5у - 7 = 0

{3х + 8у + 21 = 0

{х + 5у = 7

{3х + 8у = -21

{х = 7 - 5у

{3х + 8у = -21

1)

3х + 8у = -21

3(7 - 5у) + 8у = -21

21 - 15у + 8у = -21

-15у + 8у = -21 - 21

-7у = -42

у = -42 : (-7)

у = 6

2)

х = 7 - 5у

х = 7 - 5 * 6

х = 7 - 30

х = -23

[tex]\displaystyle\bf\\\left \{ {{x + 5y - 7 = 0} \atop {3x + 8y + 21 = 0 }} \right. \\ \displaystyle\bf\\\left \{ {{x = 7 - 5y} \atop {3(7 - 5y) + 8y = - 21 }} \right. \\ \\ 21 - 15y + 8y = - 21 \\ - 7y = - 21 - 21 \\ - 7y = - 42 \\ y = - 42 \div ( - 7) \\ y = 6 \\ \\ x = 7 - 5 \times 6 \\ x = 7 - 30 \\ x = - 23[/tex]

Ответ: ( - 23 ; 6 )