sin21°cos81°+cos189°sin69°化简

分类: 作业答案 • 2022-05-02 23:53:55

问题描述：

答

sin21°cos81°+cos189°sin69°
=sin21°cos81°-cos9°sin69°
=sin21°sin9°-cos9°cos21°
=-cos(9+21)°
=-cos30°
=-√3/2