I am stuck on trying to prove a trig identity using De Moivre's theorem.
I have to prove, $$\cos(3\theta) = 4\cos^3(\theta) - 3\cos(\theta)$$
I am not sure where to even start, I broke the LHS down to $$\cos(3\theta) + i\sin(3\theta)$$
but I have no idea where to go from here, or if this is fully correct.
If I could get some pointers or a simple worked example that I could follow it would be great.