(sin39° -sin21°)/(cos39°-cos21°)

来源：学生作业帮编辑：大师作文网作业帮分类：数学作业时间：2024/11/17 13:44:16

sin39° -sin21°
=sin(60°-21°)-sin21°
=√3/2*cos21°-1/2*sin21°-sin21°
=√3/2*cos21°-3/2 sin21°
=√3(1/2 *cos21°-√3/2 sin21°)
cos39°-cos21°
=cos(60°-21°)-cos21°
=1/2 cos21°+√3/2 sin21°-cos21°
=√3/2 sin21°-1/2 cos21°
所以原式= - √3

1.比大小：tan21°和tan31°；2.sin21°和cos21°；3.cos21°和cos22° 化简：cos21°+cos22°+cos23°+…+cos289°．计算：sin21°+sin22°+sin23°+…+sin287°+sin288°+sin289°．计算：sin21°+sin22°+sin23°+…+sin288°+sin289°+sin290°= ___ ．不求值,分别比较下列各组中两个三角函数值的大小(1)sin21/5π与sin42/5π sin1/5与cos5 森冄°仺芊 ° 0° 30° 45° 60° 90° 120° 135° 150° 180° 210° 225° 240° 270° 3 tan30° sin30° cos30° tan60° sin60° cos60° tan45° 计算:tan1°*tan2°*tan3°*tan4°.tan87°*tan88°*tan89°. 左上角句号怎么打° ° ° ° ° ° ° 怎么打出来的 cos30°,45°60° tan60°45°30° sin30°60°45° 化简sin12°×sin48°×sin54°?