\(x^2-y^2-3x+3y\)
\(=\left(x^2-y^2\right)-3\left(x-y\right)\)
\(=\left(x-y\right)\left(x+y\right)-3\left(x-y\right)\)
\(=\left(x-y\right)\left(x+y-3\right)\)
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