cosπ/5×cos2π/5

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cosπ/5×cos2π/5
cosπ/5×cos2π/5

cosπ/5×cos2π/5
cosπ/5×cos2π/5=(2sinπ/5cosπ/5×cos2π/5)/2sinπ/5=(2sin2π/5×cos2π/5)/(4sinπ/5)
=(sin4π/5)/(4sinπ/5)=1/4

cosxcosy-sinxsiny=cos(x+y)
cosxcosy+sinxsiny=cos(x-y)
2cosxcosy=cos(x+y)+cos(x-y)
2cos∏/5cos2∏/5=cos(3∏/5)+cos(∏/5)
cos∏/5cos2∏/5={cos(3∏/5)+cos(∏/5)}/2

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 怎样变成 cosπ/5 + cos2π/5rt （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. 若cos(π-θ)=3/5,cos2θ= cos(π-θ)=3/5 求cos2θ cos(π- θcos2θ)=3/5 求 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 +cos3π/5 +cos4π/5 =可以简写. 求cosπ/5乘cos2π/5乘cos3π/5乘cos4π/5