Toán Lớp 9: $\left \{ {{4x+y=-5} \atop {3x-2y=-12}} \right.$
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Toán Lớp 9: $\left \{ {{4x+y=-5} \atop {3x-2y=-12}} \right.$
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Đáp án
$\begin{cases} 4x + y = -5 \\ 3x – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} 8x + 2y = -10 \\ 3x – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} 8x + 2y + 3x + 2y = -10 + ( -12 ) \\ 3x – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} 11x = -22 \\ 3x – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} x = -2 \\ 3 . ( -2 ) – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} x = -2 \\ -6 – 2y = -12 \\\end{cases}$
⇔ $\begin{cases} x = -2 \\ 2y = 6\\\end{cases}$
⇔ $\begin{cases} x = -2 \\ y = 3 \\\end{cases}$
Vậy x = -2 ; y = 3