Solution #10: Simple Algebra
There was nothing wrong up through line
(x + y)(x - y) = y (x - y)
If we substitute the values of x and y we have
(2)(0) = (1)(0)
0 = 0
However, when we divide both sides by (x - y), we break a fundamental rule of mathematics that we cannot divide out by a fraction which is equal to zero.
: Longley-Cook, L. H.
: Reasoning, Algebra, Pitfall, Favorite