Elimination method means you're essentially. "subtracting" one equation from another.
x-y=17
- x+y=-1
---------
-2y=18
Now we'll solve x+y=-1 and -2y=18 separately.
-2y=18
Divide both sides by -2.
y=-9
x-9=-1
Add 9 to both sides.
x=8
The solutions are x=8 and y=-9, or (8,-9).
