If cos4x=1/4, evaluate the following;
a) cosx^4-sinx^4
A.Maths
2006-10-23 3:03 am
回答 (1)
2006-10-23 3:21 am
✔ 最佳答案
cos4x=1/4cosx^4-sinx^4
=(cosx^2+sinx^2)(cosx^2-sinx^2)
=(cosx^2-sinx^2)
=cos2x
since
cos4x=1/4
2cos(2x)^2-1=1/4
2cos(2x)^2=5/4
cos(2x)^2=5/8
cos2x=square root(5/8)
cosx^4-sinx^4
=square root(5/8)
收錄日期: 2021-04-13 16:02:33
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20061022000051KK04665