Alas, you won't be able to find that by hand, there's where the calculator comes handy.
There are certain angles easily found, but this is not the case.
I have the solve the following equation without using a calculator:
2cos2x=1+cosx, where x is in radians and between 0 and 2 pi.
I used the double angle formulae to get that:
(4cosx +3)(cosx -1)=0,
But how can I figure out what cosx = -3/4 is?
Con somebody help me? Is there an easier way of doing it? Any help is very much appreciated.