prove that
cos(2a+b)+cosb = 2cosacos(a+b)
trigo (3)
2007-03-19 9:39 pm
回答 (1)
2007-03-19 10:10 pm
✔ 最佳答案
Using formula cosA + cosB = 2 cos[(A + B)/2] cos[(A - B)/2]
L.H.S.
= cos(2a+b)+cosb
= 2 cos[(2a + b + b)/2] cos[(2a + b - b)/2]
= 2 cos[(2a + 2b)/2] cos[2a/2]
= 2 cos(a + b) cos a
= 2cosacos(a+b)
= R.H.S.
參考: Me
收錄日期: 2021-04-12 23:47:42
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070319000051KK01429