secФ=2 is the same as cosФ=1/2 because sec and cos are inverse functions.
So when solving cosФ=1/2, you need the find the angles where the cos graph equals 1/2. Generally you're supposed to memorize some angle values for your trig functions and this is one of them. The cosine graph is equal to 1/2 when Ф=60° or pi/3 in radians. The answer is also 300° or 5pi/3 radians because cosine is also positive in the fourth quadrant.
Hope this helps
