Hi,

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.