Write the solution set of the equation (2 cos x + 1) (4 cos x + 5) = 0 in the interval (0, 2 π].
8 cos2x+10 cos x+4 cos x+5=0
8 cos2x+14 cos x+5=0
Solving the quadratic equation, we get,
cos x = -0.5
cos x = cos 120°
So
And when n=1