Answer: B) Infinitely many solutions; both equations are equivalent
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Work Shown:
x+y = 4 ... start with the first equation
x + (-x+4) = 4 ... replace y with (-x+4)
x-x+4 = 4
0x+4 = 4
0+4 = 4
4 = 4 ... this is a true statement regardless of what x you pick
So there are infinitely many solutions. Each solution (x,y) is of the form (x,-x+4). All solutions fall on the line y = -x+4 which is equivalent to x+y = 4. Note how we add x to both sides.
Or you could start with x+y = 4 and subtract x from both sides to get y = -x+4. Either way, we're dealing with the same equation which is why they both graph out the same line.
