Given the system of equation
[tex]\begin{gathered} -2x+y-2z=-8\ldots\ldots\ldots\text{.}(1) \\ 7x+y+z=-1\ldots\ldots\ldots\text{..}(2) \\ 5x+2y-z=-9\ldots\ldots\ldots\text{.}(3) \end{gathered}[/tex]step 1: Make z the subject of the formula in equations (2)
[tex]z=-1-7x-y\ldots\ldots\ldots(2)[/tex]step 2: Substitute the value of z obtained into equation (1)
10
step 3: Substitute the value of z obtained in step 1 into equation (3)
[tex]\begin{gathered} 5x+2y-(-1-7x-y)=-9 \\ 5x+2y+1+7x+y=-9 \\ 12x+3y=-10\ldots\ldots\ldots\text{.}(5) \end{gathered}[/tex]step 4: Solve equations (4) and (5) simultaneously,
[tex]\begin{gathered} 12x+3y=-10\ldots\ldots\ldots\text{.}(4) \\ 12x+3y=-10\ldots\ldots\ldots\text{.}(5) \\ \text{subtract equation (5) from (4)} \\ (12x-12x)+(3y-3y)=-10-(-8) \\ 0\text{ + 0 = }-10+10 \\ 0=0 \end{gathered}[/tex]Therefore, the system has infinite solutions
The solution in terms of z is
[tex]\begin{gathered} x=-\frac{1}{3}z+\frac{7}{9} \\ y=\frac{4}{3}z-\frac{58}{9} \\ z=z \end{gathered}[/tex]