Ответ:

  1. По свойствам степеней: \(a^{9+12-17}=a^4=2^4=16\).
  2. \(b^{13+11-21}=b^3=3^3=27\).
  3. \(c^{5\cdot4-16}=c^4=4^4=256\).
  4. \(d^{6\cdot3-15}=d^3=5^3=125\).
  5. \(x^{8\cdot2+5-19}=x^2=6^2=36\).
  6. \(y^{5\cdot5+6-28}=y^3=7^3=343\).
  7. \(a^{19-8-9}=a^2=2^2=4\).
  8. \(b^{21-8-11}=b^2=3^2=9\).
  9. \(c^{-15-(-18)}=c^3=4^3=64\).
  10. \(d^{-9+2\cdot6}=d^3=5^3=125\).
  11. \(x^{16-7-6}=x^3=6^3=216\).
  12. \(y^{18-6-10}=y^2=7^2=49\).