$\left \{ {{3x - 4y = 8} \atop { x/10 + y/4 = - 0, 5}} \right.$
<=> $\left \{ {{3x - 4y = 8} \atop { x + 5y = - 10}} \right.$
<=> $\left \{ {{3x - 4y = 8} \atop { 3x + 15y = - 30}} \right.$
<=> $\left \{ {{3x - 4y = 8} \atop { -19y =38}} \right.$
<=> $\left \{ {{3x - 4.(-2) = 8} \atop { y =-2}} \right.$
<=> $\left \{ {{3x +8 = 8} \atop { y =-2}} \right.$
<=> $\left \{ {{3x =0} \atop { y =-2}} \right.$
<=> $\left \{ {{x = 0} \atop { y =-2}} \right.$
.
$\left \{ {{2 ( x - 3y ) = 3 - y } \atop {2x - 9y = 6 - ( 2x - y )}} \right.$
<=> $\left \{ {{2 x - 6y = 3 - y } \atop {2x - 9y = 6 - 2x + y }} \right.$
<=> $\left \{ {{2 x - 5y = 3 } \atop {4x - 10y = 6 }} \right.$
<=> $\left \{ {{4 x - 10y = 6 } \atop {4x - 10y = 6 }} \right.$
=> PT có vô số nghiệm
