Đáp án:a)$\left \{ {{y=1} \atop {x=1}} \right.$
b)$\left \{ {{y=4} \atop {x=3}} \right.$
c)$\left \{ {{y=6} \atop {x=4}} \right.$
d)$\left \{ {{y=\frac{29}{11}} \atop {x=\frac{28}{11}}} \right.$
Giải thích các bước giải:
a)$\left \{ {{x+y=2} \atop {2x-3y=9}} \right.$⇔ $\left \{ {{2x+2y=4} \atop {2x-3y=9}} \right.$
⇔$\left \{ {{5y=5} \atop {x+y=2}} \right.$⇔ $\left \{ {{y=1} \atop {x=1}} \right.$
b)$\left \{ {{x+2y=11} \atop {5x-3y=3}} \right.$⇔ $\left \{ {{5x+10y=55} \atop {5x-3y=3}} \right.$
⇔$\left \{ {{13y=52} \atop {5x-3y=3}} \right.$⇔ $\left \{ {{y=4} \atop {x=3}} \right.$
c)$\left \{ {{\frac{x}{y}=\frac{2}{3}} \atop {x+y-10=0}} \right.$⇔ $\left \{ {{3x-2y=0} \atop {x+y=10}} \right.$⇔ $\left \{ {{3x-2y=0} \atop {3x+3x=30}} \right.$⇔ $\left \{ {{y=6} \atop {x=4}} \right.$
d)$\left \{ {{3x-y=5} \atop {2x-3y=13}} \right.$⇔ $\left \{ {{6x-2y=10} \atop {6x-9y=39}} \right.$
⇔$\left \{ {{11y=29} \atop {3x-y=5}} \right.$⇔ $\left \{ {{y=\frac{29}{11}} \atop {x=\frac{28}{11}}} \right.$
