[tex]\displaystyle\bf\\9p^{4} q-6p^{2} q^{2} +q^{3} =q\cdot(9p^{4} -6p^{2} q+q^{2} )=\\\\\\=q\cdot\Big[(3p^{2} )^{2} -2\cdot3p^{2} \cdot q+q^{2} \Big]=q\cdot(3p^{2} -q)^{2} =\\\\\\=q\cdot(3p^{2} -q)\cdot(3p^{2} -q)[/tex]