Question 9: Factoring polynomials: \(x ^2 − 9 x − 9 y − y ^2\)

\( {x^2} – 9x – 9y – {y^2} = \left( {{x^2} – {y^2}} \right) – \left( {9x + 9y} \right) = \left( {x – y} \right)\left( {x + y} \right) – 9\left( {x + y} \right) = \left( {x + y} \right)\left( {x – y – 9} \right)\)