solve the following system equations
x + y = 1
x - 1 = 1
solve for x:
x-1=1
x=1+1
x=2
plug x=2 into the first equation & solve for y:
2+y=1
y=1-2
y=-1
x + y = 1
x - 1 = 1
x-1=1
x=1+1
x=2
plug x=2 into the first equation & solve for y:
2+y=1
y=1-2
y=-1