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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 9: Giải HPT : $\begin{cases} x+y=6\\2x+3y=13 \end{cases}$ và : $\begin{cases} 2x+3y=15\\2x+6y=6 \end{cases}$

Toán Lớp 9: Giải HPT : $\begin{cases} x+y=6\\2x+3y=13 \end{cases}$
và : $\begin{cases} 2x+3y=15\\2x+6y=6 \end{cases}$

Comments ( 2 )

  1. $1)\left \{ {{x+y=6} \atop {2x+3y=13}} \right.$
    $\left \{ {{y=6-x} \atop {2x+3(6-x)=13}} \right.$
    $\left \{ {{y=6-x} \atop {2x+18-3x=13}} \right.$
    $\left \{ {{y=6-x} \atop {-x=-5}} \right.$
    $\left \{ {{y=6-5} \atop {x=5}} \right.$
    $\left \{ {{y=1} \atop {x=5}} \right.$
    $2)\left \{ {{2x+3y=15} \atop {2x+6y=6}} \right.$
    $\left \{ {{2x=15-3y} \atop {15-3y+6y=6}} \right.$
    $\left \{ {{2x=15-3y} \atop {3y=-9}} \right.$
    $\left \{ {{2x=15-(3.-3)} \atop {y=-3}} \right.$
    $\left \{ {{2x=24} \atop {y=-3}} \right.$
    $\left \{ {{x=12} \atop {y=-3}} \right.$

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222-9+11+12:2*14+14 = ? ( )

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