MQ25 --- Trigonometry
回答 (3)
2012-06-25 1:57 am
✔ 最佳答案
Simplify Cos40°+Cos80°Sol(40+80)/2=60Cos40° +Cos80°=Cos(60°－20°)+Cos(60°+20°)=(Cos60°Cos20°+Sin60°Sin20°)+(Cos60°Cos20°－Sin60°Sin20°)=2Cos60°Cos20°=Cos20°
2012-06-24 11:16 pm
一眼就看出, 厲害!!
2012-06-24 10:28 pm
Obviously, 一眼就看出是 cos (20)。
If you want more details, here you go:
cos(40) + cos(80)
= 2 cos({80+40}/2) cos({80-40}/2)
= 2 cos (60) cos (20)
= cos (20)。
If you want more details, here you go:
cos(40) + cos(80)
= 2 cos({80+40}/2) cos({80-40}/2)
= 2 cos (60) cos (20)
= cos (20)。
收錄日期: 2021-04-13 18:46:27
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20120624000051KK00242