659. a) \(\frac{270 a^{10} b^8 c^7}{810 a^4 b^{12} c}\);

$$\frac{270 a^{10} b^8 c^7}{810 a^4 b^{12} c} = \frac{270}{810} \cdot \frac{a^{10}}{a^4} \cdot \frac{b^8}{b^{12}} \cdot \frac{c^7}{c} = \frac{1}{3} \cdot a^{10-4} \cdot b^{8-12} \cdot c^{7-1} = \frac{1}{3} \cdot a^6 \cdot b^{-4} \cdot c^6 = \frac{a^6 c^6}{3b^4}$$ Ответ: \(\frac{a^6 c^6}{3b^4}\)