Chapter 10 - Section 10.2 - Systems of Linear Equations in Several Variables - 10.2 Exercises - Page 697: 8

$x=1$ $y=4$ $z=-1$

$x+y-3z=8$ $y-3z=7$ $z=-1$ Call $x+y-3z=8$ Equation 1 Call $y-3z=7$ Equation 2 Call $z=-1$ Equation 3 Substitute Equation 3 (z=-1) in Equation 2 $y-3(-1)=7$ $y+3=7$ $y=7-3$ $y=4$ Now you have solution for Y and Z, to find X subtitute $Y=4$, $Z=-1$ in Equation 1 $x+4-3(-1)=8$ $x+4+3=8$ $x+7=8$ $x=8-7$ $x=1$