Đáp án:
ở dưới
Giải thích các bước giải:
3/a)$\left \{ {{2x-3y=8} \atop {5x+2y=1}} \right.$
⇔$\left \{ {{4x-6y=16} \atop {15x+6y=3}} \right.$
⇔$\left \{ {{19x=19} \atop {2x-3y=8}} \right.$
⇔$\left \{ {{x=1} \atop {2.1-3y=8}} \right.$
⇔$\left \{ {{x=1} \atop {y=-2}} \right.$
b)$\left \{ {{x-y=1} \atop {3x+2y=8}} \right.$
⇔$\left \{ {{2x-2y=2} \atop {3x+2y=8}} \right.$
⇔$\left \{ {{5x=10} \atop {x-y=1}} \right.$
⇔$\left \{ {{x=2} \atop {2-y=1}} \right.$
⇔$\left \{ {{x=2} \atop {y=1}} \right.$
c)$\left \{ {{2.(x-y)-3.(x+y)=5} \atop {3.(x-y)+5.(x+y)=-2}} \right.$
⇔$\left \{ {{2x-2y-3x-3y=5} \atop {3x-3y+5x+5y=-2}} \right.$
⇔$\left \{ {{-x-5y=5} \atop {8x+2y=-2}} \right.$
⇔$\left \{ {{-8x-40y=40} \atop {8x+2y=-2}} \right.$
⇔$\left \{ {{-38y=-38} \atop {8x+2y=-2}} \right.$
⇔$\left \{ {{y=1} \atop {8x+2.1=-2}} \right.$
⇔$\left \{ {{x=-2} \atop {y=1}} \right.$
