化简:=2cos[(π/4)+α]请说详细一点

cos^2α+cos^2(α+π/3)-cosαcos(α+π/3)化简 5cos^2a+4cos^2β=4cosα则cos^2a+cos^2β cos^2(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)² cos^2(π/4+α)是怎么等于(cos(π/4)cosα-sin(π/4)sinα)²的? 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) 化简sin(α-2π)+sin(-a-3π)cos(α-3π)/cos(π-α)-cos(-π-α)cos(α-4π) 化简cos（π/9）cos（2π/9）cos（3π/9)cos（4π/9）=（ ）.请说明理由哦、 化简cos(π/4-a)cos(π/4+a)= 2sinα*cosα*cos(2π-α)+cos(π+2α)*cosα*tanα化简! [sin(5π-α)cos(-π-α)]/[cos(α-π)cos(π/2+α)]化简 化简:cosα+cos(2π/3-α)+cos(2π/3+α) 【紧急求助】计算:cosα+cos(2π/3 +α)+cos（4π/3 +α） 化简cosθ+cos(θ+2π/3)+cos(θ+4π/3) cos 2π/7 +cos 4π/7 +cos 6π/7=? 请问cos(2π/7)+cos(4π/7)+cos(6π/7)=?, tan(π/4+α)=2,求1/(2cosαsinα+cos^2α) 化简(1-sin^6 a-cos^6 a)/(cos^2 a-cos^4 a)== cos(α+β)=4/5cos(α-β)=-4/5,3π/2 若cos(α+β)=4/5,cos(α+β)=-4/5,且π/2