Réponse :
[tex]\left \{ {{4x-7y=-1} \atop {-3x+4y=2}} \right.[/tex]
En faisant une combinaison : L2 = 4 L2 + 3 L1
[tex]\iff\left \{ {{4x-7y=-1} \atop {-12x+12x+16y-21y}=8-3} \right.[/tex]
[tex]\iff\left \{ {{4x-7y} \atop {-5y=5}} \right.[/tex]
[tex]\iff\left \{ {{4x-7y=-1} \atop {y=-1}} \right.[/tex]
[tex]\iff\left \{ {{4x=-1+7y} \atop {y=-1}} \right.[/tex]
[tex]\iff\left \{ {{4x=-1+7*(-1)} \atop {y=-1}} \right.[/tex]
[tex]\iff \left \{ {{4x=-1-7} \atop {y=-1}} \right.[/tex]
[tex]\iff\left \{ {{4x=-8} \atop {y=-1}} \right.[/tex]
[tex]\iff\left \{ {{x=-2} \atop {y=-1}} \right.[/tex]
