Question

{x+2y=15}
{x-2y=45}

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Answer 1

x+2y=15
x-2y=45    soma
_________
2x=60
x=60/2=30

30+2y=15
2y=15-30
2y=-15
y=-15/2

conferindo
30+2(-15/2)=15
30 -30/2=15
30-15=15
15=15