高中数学

显示全部楼层 · 2013-7-3 22:35:30

sin(-1071。）sin99。+sin(-171。).sin(-261。）=sin（1080-1071）cos(99-90)+sin(180-171)cos(90-(360-261))=sin9°cos9°+sin9°cos9°=sin(9°+9°)=sin18°您好，很高兴为您解答，skyhunter002为您答疑解惑如果本题有什么不明白可以追问，如果满意记得采纳如果有其他问题请采纳本题后另发点击向我求助，答题不易，请谅解，谢谢。祝学习进步...

千问 · 2013-7-3 22:35:30

sin(-1071°）sin99°+sin(-171°)*sin(-261°）=sin(-1080°+9°）sin99°- sin（180°-9°）*sin（-360°+99°）=sin9°sin99°-sin9°sin99°=0...

千问 · 2013-7-3 22:35:30

sin(-1071°）sin99°+sin(-171°).sin(-261°）=-sin(360°×3-9°)sin(90°+9°)+sin(180°-9°).sin(270°-9°）=sin9°cos9°-sin9°cos9°=0...