Ответ:

  1. \(0{,}0000087=8{,}7\cdot10^{-6}\).
  2. \(0{,}00000005086=5{,}086\cdot10^{-8}\).
  3. \(\frac1{125}=0{,}008=8\cdot10^{-3}\).
  4. \(\frac1{625}=0{,}0016=1{,}6\cdot10^{-3}\).