SOLUTION: Solve the system by the addition method. x+y=-1 x-y=17

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Question 768617: Solve the system by the addition method.
x+y=-1
x-y=17
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!
x%2By=-1
x-y=17
________________add both
x%2By%2Bx-y=-1%2B17
2x%2Bcross%28y%29-cross%28y%29=16
2x=16
x=16%2F2
x=8
now find y
x%2By=-1
8%2By=-1
y=-1-8
y=-9