Solution 10357: Unexpected Results Returned Performing Temperature Conversions with Negative Numbers on the TI-85 and TI-86.
Why do I get the wrong answer when I perform metric conversions with negative numbers on my TI-85 or TI-86?
Conversions are of lower precedence than negation in the order of operations on the TI-85 and TI-86. Therefore, a conversion will be performed after negation. The negative number will need to be enclosed in parenthesis to receive the expected answer.
For example, -40°C>°F, will return -104 as the answer and (-40)°C>°F, will return -40, the expected answer. Please refer to the steps provided below.
• Press [(] [(-)]   [)]
• Press [2nd]  to access the conversion menu (CONV)
• Press [F5] for the TEMP menu
•Press [F1] for °C (Celsius), the conversion symbol will populate behind the °C
• Press [F2] for °F (Fahrenheit), press [ENTER] and the result will be displayed.Please see the TI-85 and TI-86 guidebooks for additional information.