[tex] (cosx)^{2} = 1/4[/tex] <=> cosx = +1/2 or cosx = -1/2;
cosx = +1/2 => x = +π/3 + 2kπ, where k is an integer or x = -π/3 + 2kπ, where k is an integer;
cosx = -1/2 => x = +2π/3 + 2kπ, where k is an integer or x = -2π/3 + 2kπ, where k is an integer;
