Chapter 3 Linear Systems and Matrices - 3.4 Solve Systems of Linear Equations in Three Variables - 3.4 Exercises - Mixed Review - Page 185: 59

$x=0$ and $y=7$

$3x-y=-7$ $/\times(3)$ to get rid of the $y$ $2x+3y=21$ _________________ $9x-3y=-21$ $2x+3y=21$ _________________ $11x=0$ $x=\frac{0}{11}$ $x=0$ when $x=0$... $2(0)+3y=21$ $0+3y=21$ $3y=21$ $y=\frac{21}{3}$ $y=7$