trigonometry(2)
回答 (2)
2011-05-27 6:37 am
✔ 最佳答案
[(cosA)^4]-[(sinA)^4]= [(cosA)^2 - (sinA)^2][(cosA)^2 + (sinA)^2]= cos2A = 1/4
2011-05-27 6:37 am
cos^4 A - sin^4 A
= (cos^2 A)^2 - (sin^2 A)^2
= [(1/2)(1 + cos2A)]^2 - [(1/2)(1 - cos2A)]^2
= [(1/2)(1 + 1/4)]^2 - [(1/2)(1 - 1/4)]^2
= 25/64 - 9/64
= 1/4
= (cos^2 A)^2 - (sin^2 A)^2
= [(1/2)(1 + cos2A)]^2 - [(1/2)(1 - cos2A)]^2
= [(1/2)(1 + 1/4)]^2 - [(1/2)(1 - 1/4)]^2
= 25/64 - 9/64
= 1/4
收錄日期: 2021-04-13 17:59:44
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110526000051KK01180