Question 1087356
Add R1 and R2,
{{{x+y-z+3x-y+z=2+2}}}
{{{4x=4}}}
{{{x=1}}}
So then the equations become,
4.{{{y-z=1}}}
5.{{{-y+z=-1}}}
{{{-4y+2z=-36}}}
6.{{{-2y+z=-18}}}
Adding 4 and 6,
{{{y-z-2y+z=1-18}}}
{{{-y=-17}}}
{{{y=17}}}
Now solve for z using any of the equations.
The system has exactly one solution.