化簡sin100°sin(-160°) cos200°cos(-280°)得？答案是多少呢？
2005-11-01 18:05:18 · 2 個解答 · 發問者 Anonymous in 科學 ➔ 數學
sin100°=sin(90°+10°)=sin10°
sin(-160°)=--sin(180°-160°)=-sin20°
cos200°=-cos(180°+20°)=-cos20°
cos(-280°)=cos(270°-280°)=cos10°
sin100°sin(-160°) cos200°cos(-280°)
=sin10°(-sin20°)(-cos20°)cos10°
=1/4*2sin10°cos10°*2sin20°cos20°
=1/4*sin20°sin40°
2005-11-02 13:40:37 補充：
tom
3q
2005-11-02 04:20:03 · answer #1 · answered by 風之痕 5 · 0⤊ 0⤋
題目應該有錯ㄅ.應該是sin100°sin(-160°) +cos200°cos(-280°)ㄅ
2005-11-02 16:32:05 · answer #2 · answered by 黑輪 1 · 0⤊ 0⤋