\[2x + x^{2} + 2y - y^{2} = 2 \cdot (x + y) +\]
\[+ \ \left( x^{2} - y^{2} \right) = 2 \cdot (x + y) + (x - y) \cdot\]
\[\cdot (x + y) = (x + y)(2 + x - y)\]