F (x) = the maximum of cosx - (SiNx) ^ 2

F (x) = the maximum of cosx - (SiNx) ^ 2

∵ f (x) = cosx-1 + cos & sup2; X = cos & sup2; X + cosx + 1 / 4-5 / 4 = (cosx + 1 / 2) & sup2; - 5 / 4 │ cosx │≤ 1 = = > - 1 ≤ cosx ≤ 1 = = > - 1 / 2 ≤ cosx + 1 / 2 ≤ 3 / 2 = = > - 3 / 2 ≤ cosx + 1 / 2 ≤ 3