Solve for x:
cos(x+15)cos(x-15)-sinxsin(x-30)=cos165
Trigonometric function(Compound Angles)
2007-04-12 7:52 am
回答 (1)
2007-04-12 8:10 am
✔ 最佳答案
cos(x+15)cos(x-15)-sinxsin(x-30)=cos165 1/2(cos2x+cos30)+1/2[cos(2x-30)-cos30]=cos(180-15)
1/2[cos2x+cos(2x-30)]=-cos15
1/2[2cos(2x-15)cos15]=-cos15
[cos(2x-15)cos15]/cos15=-1
cos(2x-15)=-1
2x-15=2n(180)+180
2x=360n+195
x=180n+195/2
收錄日期: 2021-04-13 14:46:54
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070411000051KK06856