Solution 12061: Calculating Logs on the TI-89 Family, TI-92 Family, and Voyage™ 200 Graphing Calculators.
How do I calculate a log on the TI-89 family, TI-92 family, and Voyage 200 graphing calculators?
The Logarithm (log) function on the TI-89 family, TI-92 family, and Voyage 200 is located in the [CATALOG] menu.
To access this function:
• Press [CATALOG] [L].
• Scroll to log( , press [ENTER].
• Input the value.
• Close the parentheses and press [ENTER].
• Press [diamond key]  then the number.
If there is a different base than 10, input the number, press [,] then the base
Please see the TI-89 family, TI-92 family and Voyage 200 guidebooks for additional information.