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Let’s face it, factoring is an art, really. You might notice that y^2-4y+4 is a perfect square, namely (y-2)^2.
So then your original expression actually looks like x^2 - (y-2)^2, which is a difference of squares! So then you factor accordingly to end up with
(x - (y - 2))*(x + (y - 2)) = (x - y + 2)(x + y - x)