Question

даю 50 балов система двох линейних уравнений с двумя сменами ​

Answer 1

$\displaystyle\bf\\1)\\\\-\left \{ {{x-y=3} \atop {2x-y=8}} \right. \\--------\\-x=-5\\\\x=5\\\\y=x-3=5-3=2\\\\Otvet \ : \ \Big(5 \ : \ 2\Big)\\\\\\2)\\\\+\left \{ {{4x+5y=2} \atop {3x-5y=19}} \right.\\ ---------\\7x=21\\\\x=21:7=3\\\\5y=2-4x=2-4\cdot 3=2-12=-10\\\\y=-10:5=-2\\\\Otvet \ : \ \Big(3 \ ; \ -2\Big)$

$\displaystyle\bf\\3)\\\\-\left \{ {{2x+3y=5} \atop {2x+5y=10}} \right.\\ ---------\\-2y=-5\\\\y=-5:(-2)=2,5\\\\2x=5-3y=5-3\cdot 2,5=5-7,5=-2,5\\\\x=-2,5:2=-1,25\\\\Otvet \ : \ \Big(-1,25 \ ; \ 2,5\Big)$

Answer 2

Объяснение:

х - у = 3 | * -1

2х - у = 8

-х + у = -3

2х - у = 8

х = 5

2х - у = 8

2*5 - у = 8

10 - у = 8

у = 10 - 8

у = 2

Ответ: (5; 2)

4х + 5у = 2

3х - 5у = 19

7х = 21

4х + 5у = 2

1)

7х = 21

х = 21 : 7

х = 3

2)

4х + 5у = 2

4*3 + 5у = 2

12 + 5у = 2

5у = 2 - 12

5у = -10

у = -10 : 5

у = -2

Ответ: (3; -2)

2х + 3у = 5

2х + 5у = 10 | * -1

2х + 3у = 5

-2х - 5у = -10

-2у = -5

2х + 3у = 5

1)

-2у = -5

у = -5 : (-2)

у = 2,5

2)

2х + 3у = 5

2х + 3*2,5 = 5

2х + 7,5 = 5

2х = 5 - 7,5

2х = -2,5

х = -2,5 : 2

х = -1,25

Ответ: (-1,25; 2,5)