Another approach...
Solve the system directly:
2x - y = -3 (1)
x + y = 0 (2)
Adding these equations eliminates 'y':
3x = -3
x = -1 --> y = 1 Hence (-1,1) is a solution
There you have it.
Write the system of linear equations, use x,y,z and if necessary w,x,y,z. Once...(answered by Edwin McCravy)