21. 1) \frac{4a^{3}b^{2}}{18c^{3}} \cdot \frac{9c^{2}}{8a^{2}b^{3}};

1) \(\frac{4a^{3}b^{2}}{18c^{3}} \cdot \frac{9c^{2}}{8a^{2}b^{3}} = \frac{4 \cdot 9 \cdot a^{3}b^{2}c^{2}}{18 \cdot 8 \cdot a^{2}b^{3}c^{3}} = \frac{a}{4bc}\)

Ответ: \(\frac{a}{4bc}\)