\[a^{3}b^{2} - a^{2} + a^{2}b^{2} - a =\]
\[= a^{2}b^{2}(a + 1) - a(a + 1) =\]
\[= (a + 1)\left( a^{2}b^{2} - a \right) =\]
\[= a(a + 1)(ab^{2} - 1)\]