\[\boxed{\text{681\ (681).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \left( 2x^{2} - y \right)\left( x^{2} + y \right) =\]
\[= 2x^{4} + 2x^{2}y - yx^{2} - y^{2} =\]
\[= 2x^{4} + x^{2}y - y^{2}\]
\[\textbf{б)}\ \left( 7x^{2} + a^{2} \right)\left( x^{2} - 3a^{2} \right) =\]
\[= 7x^{4} - 21a^{2}x^{2} + a^{2}x^{2} - 3a^{4} =\]
\[= 7x^{4} - 20a^{2}x^{2} - 3a^{4}\]
\[\textbf{в)}\ \left( 11y^{2} - 9 \right)(3y - 2) =\]
\[= 33y^{3} - 22y^{2} - 27y + 18\]
\[\textbf{г)}\ \left( 5a - 3a^{3} \right)(4a - 1) =\]
\[= 20a^{2} - 5a - 12a^{4} + 3a^{3}\ \]