So is there a proof that's within range of the mx2 course? The proof I've seen used Taylor series, but I've only got a vague understanding of how they work.
That seems quite harsh. I'm not sure though. And yes, it should be equal to as well, just a typo.
EDIT: Fuck, on second consideration, I might've just put > in the exam. :'(
Use the double angle formula to expand it and then draw up a right angled triangle with sides 2 and 3, find the 3rd side and use that to find sin(arccos(2/3))