a)
2x-3y=15
3x+y=6
2x-3y=15
9x+3y=18
11x=33
x=3 d'où y=-3
b)
2x-8y=4
-3x+12y=-6
6x-24y=12
-6x+24y=-12
0x+0y=0 indéterminé
c)
6x+9y = 4
-8x-12y = 8
24x+36y = 16
-24x-36y = 24
0x+0y = 24 impossible
d)
3x - y = 1
x + 5y = -3
15x - 5y = 5
x + 5y = -3
16x = 2
8x = 1
x=1/8