@FanRapital
Đáp án :
a ) Ta có : $\left \{ {{3x-y=4} \atop {4x +2y=12}} \right.$
= > $\left \{ {{6x-2y=8} \atop {4x +2y=12}} \right.$
=> $\left \{ {{10x=20} \atop {4x +2y=12}} \right.$
=> $\left \{ {{x=2} \atop {4.2 +2y=12}} \right.$
=>$\left \{ {{x=2} \atop {y=2}} \right.$
Vậy hpt có nghiệm duy nhất ( x , y ) = ( 2 , 2 )
b) Ta có : $\left \{ {{2x + 3y =6} \atop {x-2y=4}} \right.$
=> $\left \{ {{2x + 3y =6} \atop {2x-4y=8}} \right.$
=> $\left \{ {{7y =-2} \atop {2x-4y=8}} \right.$
=> $\left \{ {{y=\frac{-2}{7}} \atop {2x-4y=8}} \right.$
=> => $\left \{ {{y=\frac{-2}{7}} \atop {{x=\frac{-24}{7}} \right.$
