求值:cos2π7
求值:cos2π7
求值:cos2α+cos2(α+120°)+cos2(α+240°)的值为 ______.
已知cos2θ=7/25,π/2
已知cos2α=3/5,求值:cos^2α+sin^4α
求证cos2π/7+cosπ/3=cosπ/7+cos3π/7
COSπ/5乘以COS2π/5
求COSπ/5*COS2π/5
(1)求值sin2120°+cos180°+tan45°-cos2(-330°)+sin(-210°)
求值
求值,,
81.1 ,设a=sin5π/7,b=cos2π/7,c=tan2π/7,则
已知sin(π/6+a)=1/3,求sin(5/6π-a)+cos2(7/6π+a)