Разложите на множители: xy-x^2y^2+x^3y^3-a+axy-ax^2y^2.

\[xy - x^{2}y^{2} + x^{3}y^{3} - a + axy - ax^{2}y^{2} =\]

\[= \text{xy}\left( 1 - xy + x^{2}y^{2} \right) - a\left( 1 - xy + x^{2}y^{2} \right) =\]

\[= \left( 1 - xy + x^{2}y^{2} \right)(xy - a)\text{.\ }\]