The half-argument formula says that= . (See, for example, the lesson Trigonometric functions of half argument in this site). Substitute it into the original equation, and you will get - = . Now factor it: . = . Thus you get two equations: 1) = , which has two solutions = and in the given interval for . 2) = , or = 0, which has two solutions = and in the given interval for . Answer. The solutions are = , , and .