If cos 4θ=1/4 ,evaluate the following.
Cos^4θ- sin^4θ
I'm so stupid, I have many difficulties on a.maths....
a maths
2007-02-20 4:23 am
回答 (1)
2007-02-20 4:28 am
✔ 最佳答案
cos^4θ- sin^4θ=(cos^2θ+ sin^2θ)(cos^2θ- sin^2θ)
=cos^2θ- sin^2θ
=cos^2θ- (1-cos^2θ)
=2cos^2θ- 1
=cos2θ
=sqrt[1/2(cos 4θ+1)]
=sqrt[1/2(5/4)]
=sqrt[5/8]
2007-02-19 20:28:40 補充：
sqrt 即是開方根
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070219000051KK02856