Thread: TRIG: inverses

Hello-
I am currently working on a problem and I don't completely understand how to get to the correct answer.
The problem is:
find exact value of:

sin-1[cos(-2pi over 3)]

(sorry, I haven't figured out how to manipulate text.)

I figure that it's -radical 3 over 2; -pi over 3. The book says it -pi over 6. I see that cos radical 3 over 2 is pi over 6, but sin radical 3 over 2 is pi over 3. (?)
Please help.
Thanks.

from the unit circle (which you know well, correct?)



now ...