a) Thay m =3 vào hệ pt ta đc
$\left \{ {{(3-1)x + y = 3} \atop {x + (3-1)y=2}} \right.$
=> $\left \{ {{2x + y=3} \atop {x + 2y=2}} \right.$
=>$\left \{ {{2x + y=3} \atop {2x + 4y=4}} \right.$
=> $\left \{ {{2x + y=3} \atop { -3y=-1}} \right.$
=> $\left \{ {{2x + \frac{1}{3} =3} \atop { y=\frac{1}{3} }} \right.$
=> $\left \{ {{2x = -\frac{1}{3} +3} \atop { y=\frac{1}{3} }} \right.$
=> $\left \{ {{x = \frac{4}{3} } \atop { y=\frac{1}{3} }} \right.$