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Пояснение.
Решение.
\[\textbf{а)}\ \frac{12}{5x} \cdot \frac{x^{3}}{12a} = \frac{12 \cdot x³}{5x \cdot 12a} = \frac{x^{2}}{5a}\]
\[\textbf{б)}\ \frac{8c^{2}}{15m} \cdot \frac{1}{4c^{2}} = \frac{8c^{2}}{15m \cdot 4c^{2}} =\]
\[= \frac{2}{15m}\]
\[\textbf{в)}\ \frac{11a^{4}}{6} \cdot \frac{12b}{a^{5}} = \frac{11a^{4} \cdot 12b}{6 \cdot a^{5}} =\]
\[= \frac{22b}{a}\]
\[\textbf{г)}\ \frac{{4n}^{2}}{3m^{2}} \cdot \frac{9m}{2} = \frac{4n^{2} \cdot 9m}{3m^{2} \cdot 2} = \frac{{6n}^{2}}{m}\]