Question

Решите систему уравнений :
1){5x+y=13
{8x+3y=25
2){7x+y=33
{4x+y=21​

Answer 1

Ответ:

1)

$\left \{ {{5x+y=13} \atop {8x+3y=25}} \right.$

$\left \{ {{y=13-5x} \atop {8x+3y=25}} \right.$

8x+3(13-5x)=25

8x+39-15x=25

8x-15x=25-39

-7x=-14

x = $\frac{-14}{-7}$

x = 2

y=13-5(2)

y=13-10

y=3

Ответ: 2; 3

2)

$\left \{ {{7x+y=33} \atop {4x+y=21}} \right.$

$\left \{ {{7x+y=33 | *(-1)} \atop {4x+y=21}} \right.$

$\left \{ {{-7x-y=-33} \atop {4x+y=21}} \right.$

-7x-y+4x+y=-33+21

-7x+4x=-12

-3x=-12

x = $\frac{-12}{-3}$

x = 4

4(4)+y=21

16+y=21

y=21-16

y = 5

Ответ: 4; 5