Question 370091
1.{{{x + 3y -z = 2  }}}
2.{{{x -2y + 3z = 7}}}
3.{{{x + 2y - 5z = -21}}} 
Subtract eq. 1 from eq. 2,
{{{x-2y+3z-x-3y+z=7-2}}}
4.{{{-5y+4z=5}}}
Subtract eq. 1 from eq. 3,
{{{x+2y-5z-x-3y+z=-21-2}}}
5.{{{-y-4z=-23}}}
Add eq. 4 and eq. 5,
{{{-5y+4z-y-4z=5-23}}}
{{{-6y=-18}}}
{{{highlight( y=3)}}}
Then from eq. 5
{{{-3-4z=-23}}}
{{{-4z=-20}}}
{{{highlight(z=5)}}}
Then from eq. 1,
{{{x + 3(3) - 5 = 2  }}}
{{{x+4=2}}}
{{{highlight(x=-2)}}}