\[5x^{2} - 10x^{3} - 15x^{4} =\]
\[= 5x^{2}\left( 1 - \frac{10}{5}x^{3 - 2} - \frac{15}{5}x^{4 - 2} \right) =\]
\[= 5x^{2}\left( 1 - 2x - 3x^{2} \right)\]
\[Проверка:\]
\[5x^{2}\left( 1 - 2x - 3x^{2} \right) =\]
\[= 5x^{2} - 10x^{2 + 1} - 15x^{2 + 2} =\]
\[= 5x^{2} - 10x^{3} - 15x^{4};\]
\[5x^{2} - 10x^{3} - 15x^{4} =\]
\[= 5x^{2} - 10x^{3} - 15x^{4};\]
\[верно.\]