Find all solutions of the equation 2cos3x=1 in the interval [0,π).
2cos3x = 1 divide by 2
cos (3x) = 1/2
Now
cos (3x) = 1/2 at 3x = pi/3, 5pi/3 , 7pi/3, ......so
x = pi/9, 5pi/9, 7pi/9