Given that Sin x - sin y =p and cos x +cos y=q Express cos (x+y ) in terms of p and q?
回答 (1)
2015-11-21 12:33 pm
✔ 最佳答案
SolSinx－Siny=p
Sin^2 x－2SinxSiny+Sin^2 y=p^2
Cosx+Cosy=q
Cos^2 x+2CosxCosy+Cos^2 y=q^2
q^2+p^2
=(Cos^2 x+2CosxCosy+Cos^2 y)+(Sin^2 x－2SinxSiny+Sin^2 y)
=2+2Cos(x+y)
Cos(x+y)=(p^2+q^2－2)/2
收錄日期: 2021-04-18 14:04:00
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20151121023215AAUhfHk