\[\boxed{\text{616\ (616).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \frac{2}{7}x \cdot \left( 1,4x^{2} - 3,5y \right) =\]
\[= \frac{2}{7}x \cdot \frac{14}{10}x^{2} - \frac{2}{7}x \cdot \frac{35}{10}y =\]
\[= \frac{2}{5}x^{3} - xy = 0,4x^{3} - xy\]
\[\textbf{б)} - \frac{1}{3}c^{2} \cdot \left( 1,2d^{2} - 6c \right) =\]
\[= \frac{1}{3}c^{2} \cdot \frac{6}{5}d^{2} - \frac{1}{3}c^{2} \cdot ( - 6c) =\]
\[= - \frac{2}{5}c^{2}d^{2} + 2c^{3} =\]
\[= - 0,4c^{2}d^{2} + 2c^{3}\]
\[\textbf{в)}\ \frac{1}{2}ab \cdot \left( \frac{2}{3}a^{2} - \frac{3}{4}ab + \frac{4}{5}b^{2} \right) =\]
\(= \frac{1}{3}a^{3}b - \frac{3}{8}a^{2}b^{2} + \frac{2}{5}ab^{3}\)
\[= - 2a^{3}y^{7} + \frac{1}{5}a^{4}y^{6} + \frac{1}{3}a^{5}y^{5}\]