2 câu trả lời
$\left \{ {{-5x=2y} \atop {x-y=-7}} \right.$
$\left \{ {{5x+2y=0} \atop {y=x+7}} \right.$
$\left \{ {{5x+2(x+7)=0} \atop {y=x+7}} \right.$
$\left \{ {{7x=-14} \atop {y=x+7}} \right.$
$\left \{ {{x=-2} \atop {y=-2+7=5}} \right.$
Ta có: \(\Leftrightarrow x-1=9\) \(\Leftrightarrow x=y-7\)
\(\Rightarrow \frac{x}{2}=\frac{y}{-5}\)
\(\Leftrightarrow \frac{y-7}{2}=\frac{y}{-5}\)
\(\Leftrightarrow -5(y-7)=2y\)
\(\Leftrightarrow -5y+35=2y\)
\(\Leftrightarrow 7y=35\)
\(\Leftrightarrow y=5\)
\(\Rightarrow x=y-7=5-7=-2\)
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