91Ó°ÊÓ

The given system of equations is

$\left\{\begin{array}{l}x+2y-z=-3\\ 2x-4y+z=-7\\ -2x+2y-3z=4\end{array}\right.$

The determinant D of the coefficients of the variables

$$\begin{gathered} D=\left|\begin{array}{ccc}1& 2& -1\\ 2& -4& 1\\ -2& 2& -3\end{array}\right| \\ D={(-1)}^{1+1}\left(1\right)\left|\begin{array}{cc}-4& 1\\ 2& -3\end{array}\right|+{(-1)}^{1+2}\left(2\right)\left|\begin{array}{cc}2& 1\\ -2& -3\end{array}\right|+{(-1)}^{1+3}(-1)\left|\begin{array}{cc}2& -4\\ -2& 2\end{array}\right| \\ D=1(12-2)-2(-6+2)-1(4-8) \\ D=10+8+4 \\ D=22 \end{gathered}$$

$D≠0,$so Cramer's rule can be used to determine the solution of the system of equations.

so that$x=\frac{D_x}{D},y=\frac{D_y}{D},z=\frac{D_z}{D}$

Determine $D_x$by replacing the coefficients of x in Dwith the constants

$$\begin{gathered} D_x=\left|\begin{array}{ccc}-3& 2& -1\\ -7& -4& 1\\ 4& 2& -3\end{array}\right| \\ {D}_x={(-1)}^{1+1}(-3)\left|\begin{array}{cc}-4& 1\\ 2& -3\end{array}\right|+{(-1)}^{1+2}\left(2\right)\left|\begin{array}{cc}-7& 1\\ 4& -3\end{array}\right|+{(-1)}^{1+3}(-1)\left|\begin{array}{cc}-7& -4\\ 4& 2\end{array}\right| \\ {D}_x=-66 \end{gathered}$$

Determine $D_y$by replacing the coefficients of y in Dwith the constants

$$\begin{gathered} D_y=\left|\begin{array}{ccc}1& -3& -1\\ 2& -7& 1\\ -2& 4& -3\end{array}\right| \\ {D}_y={(-1)}^{1+1}\left(1\right)\left|\begin{array}{cc}-7& 1\\ 4& -3\end{array}\right|+{(-1)}^{1+2}(-3)\left|\begin{array}{cc}2& 1\\ -2& -3\end{array}\right|+{(-1)}^{1+3}(-1)\left|\begin{array}{cc}2& -7\\ -2& 4\end{array}\right| \\ {D}_y=11 \end{gathered}$$

Determine $D_z$by replacing the coefficients of z in Dwith the constants

$$\begin{gathered} D_z=\left|\begin{array}{ccc}1& 2& -3\\ 2& -4& -7\\ -2& 2& 4\end{array}\right| \\ {D}_z={(-1)}^{1+1}\left(1\right)\left|\begin{array}{cc}-4& -7\\ 2& 4\end{array}\right|+{(-1)}^{1+2}\left(2\right)\left|\begin{array}{cc}2& 1\\ -2& -3\end{array}\right|+{(-1)}^{1+3}(-1)\left|\begin{array}{cc}2& -7\\ -2& 4\end{array}\right| \\ {D}_z=22 \end{gathered}$$

Solution for x

$$\begin{gathered} x=\frac{D_x}{D} \\ x=\frac{-66}{22} \\ x=-3 \end{gathered}$$

Solution for y

$$\begin{gathered} y=\frac{D_y}{D} \\ y=\frac{11}{22} \\ y=\frac{1}{2} \end{gathered}$$

Solution for z

$$\begin{gathered} z=\frac{D_z}{D} \\ z=\frac{22}{22} \\ z=1 \end{gathered}$$

So the solution of the system of equations isrole="math" localid="1647374552057" $\left(-3,\frac{1}{2},1\right)$