Prove that
sin( nx) sin( x) = cos (n-1) x - cos( x) cos (nx)
thanks a lot for your help!!
F5 Amaths
2007-12-01 2:25 am
回答 (1)
2007-12-01 2:33 am
✔ 最佳答案
sin( nx) sin( x)=-1/2[cos(n+1)x-cos(n-1)x]
=-1/2[cos( x) cos (nx)-sin( nx) sin( x)-cos(n-1)x]
1/2sin( nx) sin( x)=-1/2[cos( x) cos (nx)-cos(n-1)x]
sin( nx) sin( x)=)=-[cos( x) cos (nx)-cos(n-1)x]
sin( nx) sin( x)=)=cos(n-1)x-cos( x) cos (nx)
收錄日期: 2021-04-25 17:19:00
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071130000051KK02167