化简cos^2B+cos^2(2/3Π-B) 答案是1-1/2sin(2B-Π/6)

cos^2α+cos^2(α+π/3)-cosαcos(α+π/3)化简 化简cos²B+cos²（2π/3-B） 化简cos(a+b)cos(a-b)+sin^2b 化简：2cos(A+B)cosB-cos(2A+B) 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证：1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a) 计算：cos（π/5)+cos（2π/5)+cos(3π/5)+cos(4π/5) 化简sin^2acos^b-cos^2asin^2b+cos^a-cos^2b 化简:cosα+cos(2π/3-α)+cos(2π/3+α) 化简cosθ+cos(θ+2π/3)+cos(θ+4π/3) 若COS(A+B)COS(A-B)=1/3,则COS^2A-COS^2B=多少 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) 化简cos^2B+cos^2(2/3Π-B) 答案是1-1/2sin(2B-Π/6) 求和：cos(0)+cos(α)+cos(2α)+cos(3α)+……cos(nα) 已知A+B=2/3π,则cos^2A+cos^2B的最大值 已知cos(a+b)=4/5,cos(a-b)=-4/5,3π/2 .已知Cos(a+b)=4/5,cos(a-b)= -4/5,3/2π