Ответ:

  1. \(\ln 81 \approx 4{,}3944\).
  2. \(\ln 2 \approx 0{,}6931\).
  3. \(\ln 0{,}17 \approx -1{,}7720\).
  4. \(\ln \frac{6}{7} \approx -0{,}1542\).