Answer:
x+y+4=0 and 2x-7y-21=0
Step-by-step explanation:
-7x-7y=28 {move the constant to the left-hand side and change its sign}
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-7x-7y-28=0 {Divide both sides of the equation by -7}
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x+y+4=0 ← answer
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2x-7y=21 {move the constant to the left-hand side by adding its opposite to both sides}
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2x-7y-21=21-21 {the sum of two opposites equals 0}
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2x-7y-21=0
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2x-7y-21=0 ← answer
