Question

solve x-y =2
x+y=1

Answer 1

x-y = 2
x = 2+y

substitute to next equation

Answer 2

x+y = 1
(2+y) + y = 1
2+2y=1
2y = 1-2
2y= -1
y = -(1/2)

substitue again

x-y = 2
x- (-1/2) = 2
x+1/2 = 2
x = 2- (1/2)
x = 3/2

answer: (3/2 , -1/2)