can anyone get me a little bit further with this question?
prove the identity:
cos 3x = 4cos^3x -3cosx cos 3x can also =cos(2x+x)
so far i have used the formula
cos(a+b) = cosa.cosb-sina.sinb
so this i have equated to
back to the orig equation cos2x.cosx-sin2x.sinx=4cos^3x-3cosx
so thats where i end up and i am now confused as how to proceed next!
any help appreciated.
many thanks in advance sure its nearly there.