cos²α+cos²(120°-α)+cosαcos(120°-α)化简
cos²α+cos²(120°-α)+cosαcos(120°-α)化简
化简cosα+cos(120°-α)+cos(120+α)
求证:cos²α+cos²(α+β)-2cosαcosβcos(α+β)=sin²2β
化简(sinα+cosα)²+(sinα-cosα)²
2sin²α-sinαcosα/sinαcosα+cos²α (tan=2)
若cos(α+β)cos(α-β)=1/3 则cos²α-sin²β等于
求证cos(720°+α)(2/cosα+tanα)(1/cosα-2tanα)=2cosα-3tanα
cos(75°+α)=13
sinα+cosβ=sin225° sinα-cosβ=cos225°求cos(α-β)及cos(α+β)
化简:cos(-π-α)
求和:cos(0)+cos(α)+cos(2α)+cos(3α)+……cos(nα)
怎样化简cosαcos(60°-α)+1