1, Thay $m=3$ vào, ta có: $\left \{ {{3x-2y=-1} \atop {2x+3y=1}} \right.$
⇔ $\left \{ {{9x-6y=-3} \atop {4x+6y=2}} \right.$
⇔ $\left \{ {{9x-6y+4x+6y=-3+2} \atop {y=\dfrac{1-3y}{2}}} \right.$
⇔ $\left \{ {{x=\dfrac{-1}{13}} \atop {y=\dfrac{5}{13}}} \right.$
3, Ta có: $\left \{ {{mx-2y=-1} \atop {2x+3y=1}} \right.$
⇔ $\left \{ {{3mx-6y=-1} \atop {4x+6y=2}} \right.$
⇔ $\left \{ {{3mx-6y+4x+6y=-3+2} \atop {y=\dfrac{1-3y}{2}}} \right.$
⇔ $\left \{ {{(3m+4)x=-1} \atop {y=\dfrac{1-3y}{2}}} \right.$
⇔ $\left \{ {{x=\dfrac{-1}{3m+4}} \atop {y=\dfrac{3m+7}{2.(3m+4)}}} \right.$