化简cosπ/5cos2π/5RT.

化简cosπ/5cos2π/5RT. cosπ/5 - cos2π/5 怎样变成 cosπ/5 + cos2π/5rt 求COSπ/5*COS2π/5 cosπ/5×cos2π/5= COSπ/5乘以COS2π/5 cosπ/5×cos2π/5 cosπ/5cos2π/5 cosπ/5cos2π/5=? （cosπ/5）（cos2π/5)的值等于 cosπ/5·cos2π/5等于多少? cosπ/5*cos2π/5的值等于 cosπ/5 乘以cos2π/5等于多少 若cos(π-θ)=3/5,cos2θ= cos(π-θ)=3/5 求cos2θ cos(π- θcos2θ)=3/5 求 已知,SINα=-3/5且α为第3象限,求(1)COS(π/6-α） （2）sin2α （3）COS2αRT 化简cos2α+cos2(π/3+α)+cos2(π/3-α)化简cos²α+cos²（π/3+α）+cos²（π/3-α） 已知cos(α+β)=4/5,cos(α-β)=-4/5,α+β∈（7π/4,2π）,α-β∈（3π/4,π）,求cos2αRT