COS(π/17)COS(2π/17)COS(4π/17)COS(8π/17)要过程

cos(π/17)*cos(2π/17)*cos(4π/17)*cos(8π/17) COS(π/17)COS(2π/17)COS(4π/17)COS(8π/17)要过程 倍角公式与和角公式化简或求值cos π/17 * cos 2π/17 * cos 4π/17 * cos 8π/17 求值Cos pai/17 *cos 2pai/17*cos 4pai/17*cos 8pai/17 计算：cos（π/5)+cos（2π/5)+cos(3π/5)+cos(4π/5) cos^2α+cos^2(α+π/3)-cosαcos(α+π/3)化简 求值:cos(π/11)cos(2π/11)cos(3π/11)cos(4π/11)cos(5π/11) 求值：cos(π/11)-cos(2π/11)+cos(3π/11)-cos(4π/11)+cos(5π/11) cos(π/11)cos(2π/11)cos(3π/11)cos(4π/11)cos(5π/11) ① 利用公式C（a－β)证明,cos(2π-a)=cos a 已知三角型abc三内角a b c 成等差数列,且a-c=π/3,求cos^2a+cos^2b+cos^c的值 已知sina=15/17,cosβ= - 5/13,a∈（π/2,π）,求cos（a+β）,cos（a-β）的值.急用 cos（－17/3π）＝? cos(-17/6π）= 在△ABC中,根号3cos(B+C)求根号3cos(B+C)+COS(π/2+A）的取值范围 cos(θ-π/2)等于cos(π/2-θ) 2cos(π/2+a)cos(π-a)化简 计算cos(π/5)cos(2π/5)的值