bonsoir
x + 2 y = 8
2 x + y = - 1
x = 8 - 2 y
2 ( 8 - 2 y) + y = - 1
16 - 4 y + y = - 1
- 3 y = - 1 - 16
- 3 y = - 17
y = 17/3
x + 2 *17/3 = 8
x + 34/3 = 8
3 x /3 = 24/3 - 34/3
3 x = - 10
x = - 10 /3
S ( - 10/3 ; 17/3 )
2 x+ y = - 1
2 *- 10 /3 + 17/3 = - 1
- 20 /3 + 17 /3 = - 1
- 3 /3 = - 1
- 1 = - 1