bonjour
x + y = - 5
3 x - y = 7
x = - 5 - y
3 ( - 5 - y) - y = 7
- 15 - 3 y - y = 7
- 4 y = 7 + 15
- 4 y = 22
y = - 22 /4 = - 5.5
x - 5.5 = - 5
x = - 5 + 5.5
x = 0.5
( 0.5 ; - 5.5 )
5 x + 4 y = - 40
5 x - 3 y = 30
tu multiplies la 2nde équation par - 1 de façon à éliminer les x
5 x + 4 y = - 40
- 5 x + 3 y = - 30
7 y = - 70
y = - 10
5 x + 4 *-10 = - 40
5 x = - 40 + 40
5 x = 0
x = 0
( 0 : - 10 )
2 x + y /2 = - 7/2
6 x /4 + y = - 15/4
2 x + 0.5 y = - 3.5
3 x /2 + y = - 3.75
2 x + 0.5 y = - 3.5
1.5 x + y = - 3.75
y = - 3.75 - 1.5 x
2 x + 0.5 ( - 3.75 - 1.5 x ) = - 3.5
2 x - 1.875 - 0.75 x = - 3.5
1.25 x = - 3.5 + 1.875
1.25 x = - 1.625
x = 1.3
2 * 1.3 + 0.5 y = - 3.5
2.6 + 0.5 y = - 3.5
0.5 y = - 3.5 - 2.6
0.5 y = - 6.1
y = - 12.2
( 1.3 ; - 12.2 )
on vérifie car complexe
2 x + y /2 = - 7/2
2 *1.3 + ( - 12.2 /2) = - 7 /2
2.6 - 6.1 = - 3.5
- 3.5 = - 3.5 donc ok
