You should be able to convert between radians and degrees quickly and efficiently without a calculator. However the TI89 can be useful in checking your work and allowing you to make up and check practice problems on your own.
You can tell whether the TI89 is currently using radians or degrees by checking the status line on the home screen.  
You can change the angle mode by pressing the key and opening the angle submenu. 
If your TI89 is in radian mode, first type the radian value, then open the Math menu (press ), choose the angle submenu (press ), then select either "8: DMS" or "9: DD" and press . (Instead of using the Math menu, you press to get the conversion symbol, and then type "DD" or "DMS" from the keyboard, or select the function from the .) 

The "DD" function returns the angle in exact degrees when you press (the upper result at right), or a decimal approximation when you press (the lower result at right).  
The "DMS" function returns degrees, minutes, and seconds. The result is the upper one at right, and the result is the lower result at right.  
If your TI89 is in degree mode, you can still indicate that a value is in radians. Following the value, access the Math menu (press ) and select "2: ^{r}" from the angle submenu (press ), then enter the conversion function "DD" or "DMS" (see above). (Note the parentheses around the value on the status line in the screen shot at right. What happens if you don't use them?) 
last update December 5, 2008 by JL Stanbrough