cosπ/7cos2π/7cos3π/7=?
来源:学生作业帮 编辑:神马作文网作业帮 分类:数学作业 时间:2024/09/28 01:21:00
cosπ/7cos2π/7cos3π/7=?
原式=sinπ/7*cosπ/7*cos2π/7*cos3π/7/sinπ/7
=2sinπ/7*cosπ/7*cos2π/7*cos(π-4π/7)/2sinπ/7
=sin2π/7*cos2π/7*(-cos4π/7)/2sinπ/7
=-2sin2π/7*cos2π/7*cos4π/7/4sinπ/7
=-sin4π/7*cos4π/7/4sinπ/7
=-2sin4π/7*cos4π/7/8sinπ/7
=-sin8π/7/8sinπ/7
=sinπ/7/8sinπ/7
=1/8
=2sinπ/7*cosπ/7*cos2π/7*cos(π-4π/7)/2sinπ/7
=sin2π/7*cos2π/7*(-cos4π/7)/2sinπ/7
=-2sin2π/7*cos2π/7*cos4π/7/4sinπ/7
=-sin4π/7*cos4π/7/4sinπ/7
=-2sin4π/7*cos4π/7/8sinπ/7
=-sin8π/7/8sinπ/7
=sinπ/7/8sinπ/7
=1/8
求证cos2π/7+cosπ/3=cosπ/7+cos3π/7
已知(sinα+sin2α+sin3α)/(cosα+cos2α+cos3α)=﹣4/tanα,且π<2α<3π/2,求
求值:cos2π7
化简:cosαcos2αcos3α
已知cos2α=-7/25,2α属于(π,3π/2).求sinα,cosα
COSπ/5乘以COS2π/5
求COSπ/5*COS2π/5
已知tan2x=-2根号2求cosx(cos3分之2π-cos2x)分之2cosx(cos2π/3-cos2x)分之2c
信号与系统中,求cos2πt+cos3πt+cos5πt 角频率与周期
已知cos2α=-25分之7,2α∈(π,2π),求sinaα,cosα,tanα的值
已知sin(α +π/4)=7√2/10,cos2α =7/25,求cosα 的值
已知cos2θ=7/25,π/2