The range of 0 to 2pi means an entire circle...so can you figure out what angle in 360 degrees has cos = ?
Hint... cos = adjacent over hypotenuse, so at what angles on the unit circle is the adjacent angle 2 and the hypotenuse ?
Regarding your answer, not quite... according to your equation, the cos of theta is positive, so it can't be in all 4 quadrants. Cosine is only positive in quadrants I and IV. However, the reference angle is 45 degrees (or pi/4) so you've got the right answers in there. It's pi/4 and 7pi/4.