3cos(4x) = 2
cos(4x) = 2/3
Remember that cosine is symmetric around 0, and do arccos(2/3) or use a table, etc.
arccos(2/3) = 48.19 deg, but because we know that it is symmetric around 0, -48.19 deg is also a solution.
Since you asked only for positive solutions, we add 360 deg to -48.19 and we get 311.81 deg as the second solution. To get the third positive solution we add 360 deg to 48.19 deg and we get 408.19.
In summary, our 3 solutions to arccos(2/3) are 48.19, 311.81, and 408.19 all in degrees.
So now we have 4x = 48.19, 311.81, 408.19 (deg) and we solve for x like in a normal algebraic question and we get: x = 12.05, 77.95, 102.05 (deg)
