okay so I get that I factor it out with difference of two squares
(sec theta - 2)(sec theta +2)=0
sec theta = 2
sec theta= -2
cos theta = 1/2 = pi/3 which gives me the solutions: (pi/3 + 2pi N) and (2pi/3 + 2pi N)
what I don't understand is this...since cos theta also = -1/2 shouldn't the solutions also include
(4pi/3+2pi N) and (5pi/3 + 2pi N)?