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?

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) 【紧急求助】计算:cosα+cos(2π/3 +α)+cos（4π/3 +α） cos 2π/7 +cos 4π/7 +cos 6π/7=? 请问cos(2π/7)+cos(4π/7)+cos(6π/7)=?, cos^2α+cos^2(α+π/3)-cosαcos(α+π/3)化简 计算：cos（π/5)+cos（2π/5)+cos(3π/5)+cos(4π/5) cos(π/17)*cos(2π/17)*cos(4π/17)*cos(8π/17) 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) 5cos^2a+4cos^2β=4cosα则cos^2a+cos^2β tan(π/4+α)=2,求1/(2cosαsinα+cos^2α) 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 已知0＜α＜π/2,且3sinα=4cosα求(sin^2α+2sinαcosα)/(3cos^2α-1)求cos^2α+sinαcosα 已知cos（π+α）=1/3,求下列三角函数值 1）cos（-α） 2）cos（2π+α） 3）cos（π-α） 4）cos（已知cos（π+α）=1/3,求下列三角函数值 1）cos（-α） 2）cos（2π+α） 3）cos（π-α） 4）cos（2π-α） 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。