\[\boxed{\text{471\ (471).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)} - 12x^{4}y^{3} =\]
\[= 6x^{2}y \cdot \left( - 2x^{2}y^{2} \right) =\]
\[= 12x^{2}y^{2} \cdot ( - x^{2}y)\]
\[\textbf{б)} - 12x^{4}y^{3} =\]
\[= 2xy \cdot ( - 3y) \cdot 2x^{3}y =\]
\[= 6x \cdot 2x^{2}y \cdot ( - xy^{2})\ \]