(cos^2 33°-cos^2 57°)/(sin21°-cos21°)
1.比大小:tan21°和tan31°;2.sin21°和cos21°;3.cos21°和cos22°
cos^2x+cos^2(x+120°)+cos^2(x+240°)
求证cos(720°+α)(2/cosα+tanα)(1/cosα-2tanα)=2cosα-3tanα
计算:2cos(-660°)-sin630°/4cos1020°+2cos(-300°)
cos²α+cos²(120°-α)+cosαcos(120°-α)化简
化简cos^2A+cos^(120°+A)+cos^2(240°+A)这个怎么化简呢?
化简cosα+cos(120°-α)+cos(120+α)
求2sin(-1110°)-sin960°+√2cos(-225°)+cos(-210°)详细步骤,
化简cos平方(θ+15°)+cos平方(θ-15°)-(√3/2)cos2θ
已知cos(75°+α)=13,则cos(30°-2α)的值为 ___ .
函数y=cos(x-5°)+3(根号2)cos(x+50°)的值域是
sinΘ-2cosΘ=0,Θ属于(0.,90°),求sinΘ、cosΘ的值.