Question

Zach solves the system x+y=-3 , x-y=1 and finds the solution (1,-2) use a graph to explain whether Zach's solution is reasonable

Answer 1

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x-y=1 (1)
x+y=3 (2) 
Add (1) and (2) to eliminate y: 
x- y + x - y =1 + 3
2x = 4
x = 4/2

x = 2 
Substitute x = 2 into (1) to find y: 
2 + y = 3
y = 3 - 2
y = 1 
The solution is (2, 1)