Proofs

find the flaw in this proof that 1=2:

x = y
multiply by x: (x^2) = xy
subtract by y^2: (x^2) – (y^2) = xy – (y^2)
factor both sides: (x + y)(x – y) = y(x – y)
divide both sides by x – y: x + y = y
substitute x = y: 2y = y
divide both sides by y: 2=1

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