Express (1+cos(5h))/12 in terms of cos (5h/2)
I know the answer is (cos^2 (5h/2))/6, but how to get it?
Thank you!
one trigo problem~
2009-12-13 8:10 am
回答 (1)
2009-12-13 8:23 am
✔ 最佳答案
長氣一點：Because cos(A + B) = cosAcosB - sinAsinB
So cos(A + A) = cos^2A - sin^2A
cos2A = cos^2A - (1 - cos^2A)
cos2A = 2cos^2A - 1
1 + cos2A = 2cos^2A
Let A = 5h/2
1 + cos[2(5h/2)] = 2cos^2(5h/2)
1 + cos(5h) = 2cos^2(5h/2)
[1 + cos(5h)]/12 = [2cos^2(5h/2)]/12
[1 + cos(5h)]/12 = [cos^2(5h/2)]/6
收錄日期: 2021-04-23 23:22:59
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20091213000051KK00035