cos3π/4,cosπ/3

已知cos-3/5(π/2,π,求cos(π/4)的值.
若函数f(x=cos^2x 2msinx-2m-1(0《x《π)的最大值为3,求m的值我怎么
求函数fx=4cosxcos(x-α)在0≤x≤π/4的值域
π/2(π,3π/2 1)θ(0,π/2,sinθcosθ,得0θ45
(sinα/2 cosα/2^2 2sin^2(π/4-α/2=