A-Best: That is very odd. I own a TI-89 Titanium and I tried the same problem you just did and I got "true". I tend to have a lot of mistakes with my TI-89 Titanium whenever I use the solve app with trigonometric functions and identities simply because I misplace some of the parenthesis; so, my suggestion to you is try placing parenthesis around the identities. In addition, perhaps you should try reseting your calculator back to defaults or using the "NewProb" feature under F6.
