cos(α+π/4)=3/5,-3/4π

计算：cos（π/5)+cos（2π/5)+cos(3π/5)+cos(4π/5) 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) cos(α+β)=4/5cos(α-β)=-4/5,3π/2 求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)(5/24)(11/24)=5/11?,而且过程和题好像都没关系。 已知sinα+cosα=4/5且3π/22,若sinα+sinβ+sinγ=0,cosα+cosβ+cosγ=0,则cos(α-β)的值 【紧急求助】计算:cosα+cos(2π/3 +α)+cos（4π/3 +α） 求证:cosαcos(π/3+α)cos(π/3-α)=cos3α如题,求证:4cosαcos(π/3+α)cos(π/3-α)=cos3α不好意思 少打个4 sin(3π+α )=1/4,求cos(π+α)/cosα[cos(π+α)-1]+cos(α-2π)/cos(α+2π)cos(π+α)+coa(-α) 函数 (4 20:28:50)cos^4 (π /8)+cos^4(3π/8)+cos^4(5π/8)+cos^4(7π/8) = cos（π/11）cos（2π/11）cos（3π/11）cos（4π/11）cos（5π/11）怎么解 已知sin(3π+α)=2cos(α-4π)求cos(π/2 -α)+5sin(π/2 +α)/2cos(π+α)-sin(-α) 锐角α、β满足α+β=3/4π,求cos²α+cos²β+√2cosαcosβ的值1.锐角α、β满足α+β=3/4π，求cos²α+cos²β+√2cosαcosβ的值2.已知tan(α/2)=1/4tan(β/2)，求证：tan[(β-α)/2]=3sinα/(5-3cosα) Cos[π/7] + Cos[2 π/7] + Cos[3 π/7] + Cos[4 π/7] + Cos[5 π/7] + Cos[6 π/7] + Cos[7π/7]过程思路 不要只有答案哦 若(4sinα-2cosα)/(5cosα+3sinα)=10,且α∈(-π/2,0)则cosα值为 为什么cos(β-α)=cos(α-β),已知sin(α- β)cosα-cos （ β- α )sin α =3/5,β是第三象限角,则sin ( β+5π/4）=因为cosα是偶函数,所以cos（β-α）=cos（α-β）,则原式=sin（α-β）cosα-cos（β-α）sinα=sin（α-β）co cos(α+π/4)=3/5,-3/4π