x + y + z = -3
x - y + 2z = -10
----------------------add
2x + 3z = - 13
x - y + 2z = -10
2x + y + z = -5
---------------------add
3x + 3z = -15
2x + 3z = -13
3x + 3z = -15.....multiply by -1
------------------
2x + 3z = -13
-3x - 3z = 15 (result of multiplying by -1)
-----------------add
-x = 2
x = -2 <===
2x + 3z = -13
2(-2) + 3z = -13
-4 + 3z = -13
3z = -13 + 4
3z = - 9
z = -9/3
z = -3 <===
x + y + z = -3
-2 + y - 3 = -3
-5 + y = -3
y = -3 + 5
y = 2 <===
solution is (-2 , 2 , -3)
