cos20°-cos40°-cos80°=______．_数学解答

cos20°-cos40°-cos80°=______．

人气：480 ℃　时间：2020-02-05 05:36:44

解答

cos20°-cos40°-cos80°=cos20°-cos（60°-20°）-cos（60°+20°）=cos20°-（cos60°cos20°+sin60°sin20°）-（cos60°cos20°-sin60°sin20°）=cos20°-cos60°cos20°-sin60°sin20°-cos60°cos20°+sin60...