\(a)\) \({x^2} - x - {y^2} – y\) \( = \left( {{x^2} - {y^2}} \right) - \left( {x + y} \right)\)\( = \left( {x + y} \right)\left( {x - y} \right) - \left( {x + y} \right)\)
\( = \left( {x + y} \right)\left( {x - y - 1} \right)\)
\(b)\) \({x^2} - 2xy + {y^2} - {z^2}\) \( = \left( {{x^2} - 2xy + {y^2}} \right) - {z^2}\)\( = {\left( {x - y} \right)^2} - {z^2}\)
\( = \left( {x - y + z} \right)\left( {x - y - z} \right)\)
