bonjour merci de m'aider !! ​

Bonjour

x - y = 4

2 x + 5 y = - 6

x  - y  =  4  ⇔ x = 4 + y

2 ( 4 + y ) + 5 y = - 6

8 + 2 y + 5 y = - 6

7 y = - 6 - 8

7 y = - 14

y = - 2

x - ( - 2 ) = 4

x + 2 = 4

x =  2

S ( 2 : - 2 )

3 a + b = 3

5 a + 2 b = - 24

3 a + b = 3 ⇔ b = 3 - 3 a

3 a + 2 ( 3 - 3 a ) = - 24

3 a + 6 - 6 a = - 24

- 3 a = - 24 - 6 = - 30

- 3 a = - 30

a = 10

3*10 + b = 3

b = 3 - 30 = - 27

S ( 3 : - 27 )

Bonsoir,

Résoudre les systèmes :

1)

L1 : { x - y = 4

L2 : { 2x + 5y = -6

L1: x - y = 4

x = 4 + y

L2: 2x + 5y = -6

2(4 + y) + 5y = -6

8 + 2y + 5y = -6

7y + 8 = -6

7y = -14

y = -14/7

y = -2

L1: x - y = 4

x - (-2) = 4

x + 2 = 4

x = 2

y = -2

x = 2

2)

L1: { 3a + b = 3

L2: { 5a + 2b = -4

L1: 3a + b = 3

b = 3 - 3a

L2: 5a + 2b = -4

5a + 2(3 - 3a) = -4

5a + 6 - 6a = -4

-a + 6 = -4

-a = -10

a = 10

L1: 3a + b = 3

3*10+ b = 3

30 + b = 3

b = -27

a = 10

b = -27

Bonne soirée.