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請教我做4c.
中三級數學問題(急!!)
2010-01-12 7:11 am
回答 (1)
2010-01-12 8:35 am
✔ 最佳答案
Prove : (cos @)^4 - (sin @)^4 = 2(cos @)^2 - 1By a), LHS = [ (cos @)^2 - (sin @)^2 ] [ (cos @)^2 + (sin @)^2]
= (cos @)^2 - (sin @)^2
By b) , (cos @)^2 - (sin @)^2
= 2(cos @)^2 - 1 = RHS
(Proved)
收錄日期: 2021-04-21 22:07:37
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100111000051KK01918