cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5*cos2π/5)/(2sinπ/5) =(2sin2π/低2部咋算的?

cosπ/5×cos2π/5= cosπ/5cos2π/5=? 求COSπ/5*COS2π/5 COSπ/5乘以COS2π/5 cosπ/5×cos2π/5 cosπ/5cos2π/5 若cos(π-θ)=3/5,cos2θ= cos(π-θ)=3/5 求cos2θ cos(π- θcos2θ)=3/5 求 cosπ/5 - cos2π/5 怎样变成 cosπ/5 + cos2π/5rt cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5*cos2π/5)/(2sinπ/5) =(2sin2π/低2部咋算的? （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 化简cosπ/5cos2π/5RT. 已知cos(α-β)=-4/5cos(α+β)=5/13,且α-β∈(π/2,π),α+β∈(3π/2,2π),求cos2α和cos2β的值 已知cos（α‐β）＝－4／5,cos（α+β）=4／5,且α‐β∈（π／2,π）,α+β∈（3π／2,2π）求cos2α,cos2β