若cos4θ=1/4,求下列各式的值。
cos⁴θ-sin⁴θ
a-maths!!!!!
2007-12-11 2:28 am
回答 (1)
2007-12-11 2:39 am
✔ 最佳答案
cos4 θ- sin4 θ= (cos2 θ+ sin2 θ)(cos2 θ﹣sin2 θ)
= cos2 θ﹣sin2 θ
= cos2 θ﹣(1﹣cos2 θ)
= 2cos2 θ﹣1
= cos2 θ
= ±√[1/2(cos 4θ+1)]
= ±√[1/2(5/4)]
= ±√(5/8)
= ±√10 / 4
收錄日期: 2021-04-23 20:32:50
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071210000051KK02635