cos(π/7)×cos(2π/7)×cos(3π/7)=?过程
来源:百度知道 编辑:UC知道 时间:2024/06/09 09:11:40
分子分母同时乘以8sin(π/7),分子便有2sin(π/7)cos(π/7)=sin(2π/7),再联合后面的,还有2sin(2π/7)cos(2π/7)=sin(4π/7)=sin(π-4π/7)=sin(3π/7)
再看一下还有2sin(3π/7)cos(3π/7)=sin(6π/7)=sin(π/7),跟分母上的约掉后剩下最后结果1/8.
cos(π/7)×cos(2π/7)×cos(3π/7)
=-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)
=-sin(4π/7)cos(4π/7)/4sin(π/7)
=-sin(8π/7)/8sin(π/7)
=sin(π/7)/8sin(π/7)
=1/8
cos(派/2)+cos(派/2)
cos(П/5).cos(2П/5)=?
求值:cos(π/13)+cos(3π/13)+cos(9π/13)
6.11-数学/1.(9)计算:COS(2∏/7)+ COS(4∏/7)+ COS(6∏/7),.
已知cos(x)=1/7 cos(x+y)=-11/14 且x,y属于(0,90) 求cos(y)
α,β为锐角,且cosα=1/7,cos(α+β)=-(11/14),cosβ=?
证明cos(pai/7)+cos(pai*3/7)+cos(pai*5/7)=0.5
cos(π/2-α)=?
已知cos(α+β)cos β+sin(α+β)sin β=1/3,且 α∈(3π/2,2π),求 cos(2α+π/4)的值.
若cos(α-π/3)=12/13,π/3<α<π/2,求cosα的值