Find the general solution : `cos 3x + cos x - cos 2x = 0`

Answer

`x = (2n+1) pi/4` or `x=2n pi pm pi/3, n in ZZ`

Explanation

`cos 3x + cos x - cos 2x = 0`

`2cos((3x+x)/2) cos((3x-x)/2)-cos 2x=0`

`2 cos2x cosx - cos2x = 0`

`cos2x(2 cosx-1)=0`

`cos 2x=0` or `cosx = 1/2`

`2x=(2n+1) pi/2` or `x=2n pi pm pi/3`

`x = (2n+1) pi/4` or `x=2n pi pm pi/3`