cos (2x) - cos (x) +1 =0 , x is between 0 DEG and 360 DEG
cos x = 1/2
x= 60 DEG ; 300 DEG
but there is two more answers : 90 DEG and 270 DEG
how to get them?
一條trigo唔識計落去!
2010-01-21 6:10 am
回答 (2)
2010-01-21 6:20 am
✔ 最佳答案
cos2x = cosx cosx – sinx sinx = 2(cosx)^2 - 1cos2x – cosx +1 = 0
2(cosx)^2 – 1 – cosx + 1 = 0
cosx(2cosx – 1) = 0
cosx = 0 or cosx = 1/2
x = 90, 270 or x = 60, 300
2010-01-21 9:12 pm
cos(2x)-cosx+1=0
2cos^2x-1-cosx+1=0
cosx(2cosx-1)=0
cosx=0 or cosx=1/2
x=90,270,60,300
2010-01-21 13:13:35 補充：
You have only 5 seconds to think it !
2cos^2x-1-cosx+1=0
cosx(2cosx-1)=0
cosx=0 or cosx=1/2
x=90,270,60,300
2010-01-21 13:13:35 補充：
You have only 5 seconds to think it !
收錄日期: 2021-04-26 14:00:01
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100120000051KK01761