\(a)\) \(4{x^2} - {y^2} + 4x + 1\) \( = \left( {4{x^2} + 4x + 1} \right) - {y^2} \)
\(= {\left( {2x + 1} \right)^2} - {y^2}\)
\( = \left( {2x + 1 + y} \right)\left( {2x + 1 - y} \right)\)
\(b)\) \({x^3} - x + {y^3} – y\) \( = \left( {{x^3} + {y^3}} \right) - \left( {x + y} \right)\)
\( = \left( {x + y} \right)\left( {{x^2} - xy + {y^2}} \right) - \left( {x + y} \right)\)
\( = \left( {x + y} \right)\left( {{x^2} - xy + {y^2} - 1} \right)\)
