Đáp án:
a)$\left \{ {{2x-3y=11} \atop {-4x+6y=8}} \right.$
$⇔\left \{ {{-4x+6y=-22} \atop {-4x+6y=8}} \right.$
$⇔\left \{ {{(-4x)+6y-(-4x)-6y=-22} \atop {-4x+6y=8}} \right.$
$⇔\left \{ {{0=-22} \atop {-4x+6y=8}} \right.$ (vô lí)
Vậy hệ pt vô nghiệm
b)$\left \{ {{3x-2y=10} \atop {x-\frac{2}{3}y=3\frac{1}{3}}} \right.$
$⇔\left \{ {{3x-2y=10} \atop {3x-2y=3}} \right.$ (vô lí)
Vậy hệ pt vô nghiệm
c)$\left \{ {{3a+b=-1} \atop {-3a+b=2}} \right.$
$⇔\left \{ {{3a+b+(-3a)+b=-1+2} \atop {-3a+b=2}} \right.$
$⇔\left \{ {{2b=1} \atop {-3a+b=2}} \right.$
$⇔\left \{ {{b=\frac{1}{2}} \atop {-3a+b=2}} \right.$
$⇔\left \{ {{b=\frac{1}{2}} \atop {a=\frac{-1}{2}}} \right.$
Vậy.................
