Ответ:

  1. \((6^4)^4:(6^5)^3=6^{16}:6^{15}=6\).
  2. \(8^3:4^4=2^9:2^8=2\).
  3. \(\dfrac{7^{14}\cdot(7^2)^3}{(7^3)^6\cdot7^2}=7^{14+6-18-2}=7^0=1\).
  4. \(\dfrac{25^3\cdot125^2}{5^{10}}=\dfrac{5^6\cdot5^6}{5^{10}}=5^2=25\).
  5. \(\dfrac{9^8\cdot7^8}{21^7}=\dfrac{3^{16}\cdot7^8}{3^7\cdot7^7}=3^9\cdot7=137781\).
  6. \(\dfrac{5^9\cdot4^6}{20^6}=\dfrac{5^9\cdot4^6}{5^6\cdot4^6}=5^3=125\).