x+2y+32x-y=4
x+y=0-3+y=4
2x-y=12x+y=-3
x+2y = 32x-y = 4 => y = 2x-4
x+2(2x-4) = 3 => x+4x-8 = 3 => 5x = 11 => x = 11/5y = 2x-4 = 2*11/5-4 = 22/5-4 = (22-20)/5 = 2/5
A toi de faire les autres.
Equation du 1er degrès !