cos(2派/7)+cos(4派/7)+cos(6派/7)=?
来源:学生作业帮 编辑:搜搜考试网作业帮 分类:数学作业 时间:2024/08/18 13:27:01
cos(2派/7)+cos(4派/7)+cos(6派/7)=?
![cos(2派/7)+cos(4派/7)+cos(6派/7)=?](/uploads/image/z/8108098-34-8.jpg?t=cos%282%E6%B4%BE%2F7%29%2Bcos%284%E6%B4%BE%2F7%29%2Bcos%286%E6%B4%BE%2F7%29%3D%3F)
Pi表示派.
cos(2pi/7)+cos(4pi/7)+cos(6pi/7)
=1/[2sin(2pi/7)]*[2sin(2pi/7)cos(2pi/7)+2sin(2pi/7)cos(4pi/7)+2sin(2pi/7)cos(6pi/7)]
进行积化和差
=1/[2sin2pi/7)]*{sin(4pi/7)+[sin(6pi/7)-sin(2pi/7)] +[sin(8pi/7)-sin(4pi/7)]}
=1/[2sin(2pi/7)][-sin(2pi/7)+sin(6pi/7)-sin(6pi/7)]
=1/[2sin(2pi/7)]*[-sin(2pi/7)]
=-1/2.
cos(2pi/7)+cos(4pi/7)+cos(6pi/7)
=1/[2sin(2pi/7)]*[2sin(2pi/7)cos(2pi/7)+2sin(2pi/7)cos(4pi/7)+2sin(2pi/7)cos(6pi/7)]
进行积化和差
=1/[2sin2pi/7)]*{sin(4pi/7)+[sin(6pi/7)-sin(2pi/7)] +[sin(8pi/7)-sin(4pi/7)]}
=1/[2sin(2pi/7)][-sin(2pi/7)+sin(6pi/7)-sin(6pi/7)]
=1/[2sin(2pi/7)]*[-sin(2pi/7)]
=-1/2.
cos(2派/7)+cos(4派/7)+cos(6派/7)=?
化简sin(13派/6)+cos(7派/3)-tan(49派/4)
求值:cos 派/7 + cos 3派/7 + cos 5派/7
cos(-派/6)+cos(派- 派/6)cos(2派- 派/6)+cos(3派- 派/6)+……+cos(2010派-
已知f(a)=[sin(a-派/2)cos(3派/2-a)tan(7派-a)]/[tan(-a-5派)sin(a-3派)
为什么cos(a-7派)=cos(派+A)
化简4sin派/8*cos派/8*(cos^2派/8-sin^2派/8)
cos(派-a)=?
已知sin(a+派)=-1/2则1/cos(a+7派)的值为
(cot(a+4派)cos(a+派)sin^2(a+3派))/(tan+(派+a)cos^3(-派-a))
求下列各三角函数值tan3分之11派,sin3分之17派,cos(-6分之7派),tan(-4分之7派),sin900℃
已知cos(a-派/6)+sina=4/5根号3,则sin(a+7/6派)的值是?