So you've got
let
a^2 - 2ab + b^2 = c^2 -2cd + d^2
therefore
(a - b)^2 = (c - d)^2
therefore
(a - b) = (c - d)
let a = 1, b = 2, c =4, d = 3
(1 - 2)^2 = (4 - 3)^2
1 = 1
Even though (1 - 2) =/= (4 - 3)
so X^2 = Y^2
-/-> X = Y
(equal squares does not imply equal values)
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