The first thing to do, obviously, is to find the first derivative, which is
First I tried factoring, then using a couple of trigonometric identities.
None of this, however, gets me any closer to . I differentiated a second time and got
I haven't double-checked my math on this last step but I'm pretty sure I'm right, but, regardless, it's not any closer either! So, I ask you, am i doing something wrong or just trying to follow the wrong steps?