Question 507278
y = -3x + 1 and 3x + y = -1

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Substitute for "y" and solve for "x":
3x + y = -1
3x +(-3x+1) = -1
1 = -1
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That is a contradiction.
Why did it happen?
You assumed the x and the y in the 2 equations 
had the same value. They don't.
There is no (x,y) that fits both equations.
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That system of two equations has no solution.
If you graphed the two equations you would
find that they are parallel: no common point.
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Cheers,
Stan H.