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HOW TO FIND SOME TRIG IDENTITIES WITH TI89 CALCULATOR

 
Steps Key Sequence Screens
1. Change Mode to Radians Press MODE
  Press down arrow key three (3) times
  Press right arrow key once
  Press 1 (for RADIAN)
  Press ENTER (to Save)
2. Clear Stored Values in Variables Press 2nd, then F1
(to select F6)
  Press 1
(for Clear a-z)
  Press ENTER
(to Clear a-z)
3. Select tCollect Function Press F2 (for Algebra menu)
  Press 9 (for Trig submenu)
  Press 2 (for
'tExpand('
)
4. Input Function  
5. Execute Press ')', then ENTER
NOTE: If the result contains an arrow at the end of the expression, use up/right arrows to view the rest of the expression.