10,$\left \{ {{x-2y=1} \atop {6x+y=6}} \right.$ 

$\left \{ {{x-2y=1} \atop {12x+2y=12}} \right.$   
$\left \{ {{13x=13} \atop {x-2y=1}} \right.$   
$\left \{ {{x=1} \atop {1-2y=1}} \right.$   
$\left \{ {{y=0} \atop {x=1}} \right.$   
vậy.....  
11,$\left \{ {{3x-2y=2} \atop {2x-y=1}} \right.$   
$\left \{ {{3x-2y=2} \atop {4x-2y=2}} \right.$     
$\left \{ {{x=0} \atop {0-y=1}} \right.$   
$\left \{ {{y=-1} \atop {x=0}} \right.$     
vậy.....
12,$\left \{ {{2x-y=3} \atop {3x+4y=10}} \right.$   
$\left \{ {{8x-4y=12} \atop {3x+4y=10}} \right.$   
$\left \{ {{11x=22} \atop {2x-y=3}} \right.$   
$\left \{ {{x=2} \atop {4-y=3}} \right.$   
$\left \{ {{y=1} \atop {x=2}} \right.$   
vậy....