a) \({x^4}y - x{y^4}\)
b) \({x^2} + 10y - 5x - 2xy\)
\(\begin{matrix} a){x^4}y - x{y^4} \hfill \\ = xy\left( {{x^3} - {y^3}} \right) \hfill \\ = xy\left( {x - y} \right)\left( {{x^2} + xy + {y^2}} \right) \hfill \\ \end{matrix}\)
\(\begin{matrix} b){x^2} + 10y - 5x - 2xy \hfill \\ = \left( {{x^2} - 5x} \right) + \left( {10y - 2xy} \right) \hfill \\ = x\left( {x - 5} \right) + 2y\left( {5 - x} \right) \hfill \\ = x\left( {x - 5} \right) - 2y\left( {x - 5} \right) \hfill \\ = \left( {x - 2y} \right)\left( {x - 5} \right) \hfill \\ \end{matrix}\)