求值:cos(2pai/7)+cos(4pai/7)+cos(6pai/7)
来源:学生作业帮 编辑:灵鹊做题网作业帮 分类:数学作业 时间:2024/05/29 07:48:24
求值:cos(2pai/7)+cos(4pai/7)+cos(6pai/7)
pai打不出,不好意思
pai打不出,不好意思
cos(2π/7)+cos(4π/7)+cos(6π/7)
=[sin(2π/7)cos(2π/7)+sin(2π/7)cos(4π/7)+sin(2π/7)cos(6π/7)]/sin(2π/7)
(下面用积化和差)
=1/2[sin(4π/7)+sin(6π/7)-sin(2π/7)+sin(8π/7)-sin(4π/7)]/sin(2π/7)
=1/2[sin(6π/7)-sin(2π/7)+sin(8π/7)]/sin(2π/7)
=1/2[-sin(2π/7)]/sin(2π/7)
=-1/2
=[sin(2π/7)cos(2π/7)+sin(2π/7)cos(4π/7)+sin(2π/7)cos(6π/7)]/sin(2π/7)
(下面用积化和差)
=1/2[sin(4π/7)+sin(6π/7)-sin(2π/7)+sin(8π/7)-sin(4π/7)]/sin(2π/7)
=1/2[sin(6π/7)-sin(2π/7)+sin(8π/7)]/sin(2π/7)
=1/2[-sin(2π/7)]/sin(2π/7)
=-1/2
cos(pai/15)×cos(2pai/15)×cos(3pai/15)×cos(4pai/15)×cos(5pai/
计算下列三角函数值!sin(-7/6pai) cos(5/4pai) tan(-16/3pai)
已知a属于(pai/2,pai),tan(a+pai/4)=1/7,sin a+cos a=?
f x =sin(pai*x/4-pai/6)-2(cos pai*x/8)^2+1
已知cos(a-pai/6)+sina=4根3/5,求sin(a+7pai/6)的值
已知cos(a-pai/6)+sina=4√3/5,则sin(a+7/6pai)的值是?
已知cos(x-pai/6)+sinx=4乘根号3/5,则sin(x+7pai)=
已知函数f(x)=1+cos2x/4sin(pai/2-x)-asinx/2cos(7pai-x/2)
[tan(pai-a)cos(2pai-a)sin(-a+3pai/2)]/[cos(-a-pai)sin(-pai-a
化简sin(-2/3pai+kpai)cos(pai/6+kpai)tan(pai/4+kpai),k属于z
sin(pai-a)cos(-8pai-a)=60/169且a属于(pai/4,pai/2)求cosa,sina
化简:[cos(a+pai)*sin^2(a+pai)]/[tan^2(pai+a)*cos^3a]