cos^2 π/8+cos ^2 3π/8+ cos^2 5π/8+cos^2 7π/8=?
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cos^2π/8+cos^23π/8+cos^25π/8+cos^27π/8=?cos^2π/8+cos^23π/8+cos^25π/8+cos^27π/8=?cos^2π/8+cos^23π/8+c
cos^2 π/8+cos ^2 3π/8+ cos^2 5π/8+cos^2 7π/8=?
cos^2 π/8+cos ^2 3π/8+ cos^2 5π/8+cos^2 7π/8=?
cos^2 π/8+cos ^2 3π/8+ cos^2 5π/8+cos^2 7π/8=?
不同那些公式,太麻烦了
因为cos(π-α)=-cos α
所以cos 7π/8= -cos π/8
cos^2 7π/8=cos^2 π/8
同理cos^2 5π/8=cos^2 3π/8
原式=2（cos^2 π/8+cos^2 3π/8）
这里用到cos(π/2-α)=sin α
显然cos^2 π/8=sin^2 3π/8
原式=2（sin^2 3π/8+cos^2 3π/8）
=2
cos²(π/8)+ cos²(3π/8)+ cos²(5π/8)+ cos²(7π/8)
=[1+cos(π/4)]/2+[1+cos(3π/4)]/2+[1+cos(5π/4)]/2+[1+cos(7π/4)]/2
=2+[cos(π/4)+ cos(3π/4)+ cos(5π/4)+ cos(7π/4)]/2
=2
cos^2 π/8+cos ^2 3π/8+ cos^2 5π/8+cos^2 7π/8=?
cos(π/17)*cos(2π/17)*cos(4π/17)*cos(8π/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)
0.5-cos^2(π/8)
cos(-2/3)π=?
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cosθ^2+cos(θ+π/3)^2-cosθcos(θ+π/3)化简如何化简
cosθ^2+cos(θ+2π/3)^2+cos(θ-2π/3)^2 计算
cos^2A+cos^2(2π/3+A)+cos^2(4π/3+A)
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求值：cos²A+cos²（2π/3+A)+cos²(2π/3-A)
化简cosθ+cos(θ+2π/3)+cos(θ+4π/3)
【紧急求助】计算:cosα+cos(2π/3 +α)+cos（4π/3 +α）
cos（π/11）cos（2π/11）cos（3π/11）cos（4π/11）cos（5π/11）怎么解