化简cosπ/7*cos2π/7*cos4π/7 提示:据分析应该用倍角公式.
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化简cosπ/7*cos2π/7*cos4π/7 提示:据分析应该用倍角公式.
化简cosπ/7*cos2π/7*cos4π/7
提示:据分析应该用倍角公式.
化简cosπ/7*cos2π/7*cos4π/7 提示:据分析应该用倍角公式.
cos(π/7)*cos(2π/7)*cos(4π/7)
=[2sin(π/7)cos(π/7)*cos(2π/7)*cos(4π/7)]/2sin(π/7)
=[sin(2π/7)*cos(2π/7)*cos(4π/7)]/2sin(π/7)
=[2sin(2π/7)*cos(2π/7)*cos(4π/7)]/4sin(π/7)
=[sin(4π/7)*cos(4π/7)]/4sin(π/7)
=[2sin(4π/7)*cos(4π/7)]/8sin(π/7)
=sin(8π/7)/8sin(π/7) (因为sin(8π/7)=-sin(π/7))
=-1/8
求值:cosπ/7*cos2π/7*cos3π/7
cosπ/7cos2π/7cos3π/7=?
cosπ/7cos2/7πcos4/7π=
求证cos2π/7+cosπ/3=cosπ/7+cos3π/7
化简cosπ/7*cos2π/7*cos4π/7 提示:据分析应该用倍角公式.
化简cos2α+cos2(π/3+α)+cos2(π/3-α)化简cos²α+cos²(π/3+α)+cos²(π/3-α)
化简cosπ/5cos2π/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=?
已知cos(π/3-α)=根号3/3,求cos(2π/3+α)+cos2(7π/6+α)
cosπ/5 - cos2π/5 怎样变成 cosπ/5 + cos2π/5rt
cosπ/7cos2π/7cos4π/7cos8π/7=?每步都写
sin3/7π*cos2/5π-cos(-3/7π)*sin(-2/5π)
求值:cosπ/7·cos2π/7·cos4π/7