a) $\left\{\begin{matrix}2x-3y+z=-7 & & \\ -4x+5y+3z=6 & & \\ x+2y-2z=5 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ 10x-14y+z=-27& & \\ 5x-4y-z=-9 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ 10x-14y+z=-27& & \\ 10x-8y-2z=-18 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ 6y=9 & & \\ 10x-8y-2z=-18 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x=0,6 & & \\ y=1,5 & & \\ z=-1,3 & & \end{matrix}\right.$
Vậy hệ trên có nghiệm $\left\{\begin{matrix}x=0,6 & & \\ y=1,5 & & \\ z=-1,3 & & \end{matrix}\right.$
b) $\left\{\begin{matrix}x+4y-2z=1 & & \\ -2x+3y+z=-6 & & \\ 3x+8y-z=12 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ -3x+10y=-11 & & \\ -5x-12y=-23 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ -15x+50y=-55 & & \\ -15x-36y=-69 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x+4y-2z=1 & & \\ -15x+50y=-55 & & \\ 86y=14 & & \end{matrix}\right.$
<=> $\left\{\begin{matrix}x=4,2 & & \\ y=0,16 & & \\ z=1,92 & & \end{matrix}\right.$
Vậy hệ trên có nghiệm $\left\{\begin{matrix}x=4,2 & & \\ y=0,16 & & \\ z=1,92 & & \end{matrix}\right.$
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