Chapter 9 Quadratic Relations and Conic Sections - 9.3 Graph and Write Equations of Circles - 9.3 Exercises - Mixed Review - Page 632: 73

See below

Given: $2x+5y-z=-7\\x+3y+2z=12\\-x+2y=5$ Multiply the first equation by $2$ and add it to the second: $5x+13y=-2$ We have the new system: $5x+13y=-2\\-x+2y=5$ Multiply the second equation by $5$ and add it to the first one: $23y=23\\y=1$ Find $x$: $-x+2(1)=5\\x=-3$ Find $z$: $2(-3)+5(1)-z=-7\\z=6$