1-cosX=-sinX
1-2cosX-2cos(2)X=sin(2)X
1-2cosX+2cos(2)X-[1-cos(2)X]=0
2cosX+2cos(2)X=0
點解下一步
2cosX=-2cos(2)X
1=-cosX
係錯?
注:(2)<-2次方
cos的除數問題
2008-04-10 8:59 pm
回答 (2)
2008-04-10 10:16 pm
✔ 最佳答案
錯的原因是若X=90/270....., cosX = 0,那樣便不能兩邊一起除cosX,因除0是undefined的.
2008-04-10 9:04 pm
From 2cosX+2cos(2)X=0,
2cosX (1+cosX)=0
ie: 2cosX=0 or 1+cosX=0
Ans: X=90 degree or (pi)/2 or X= 180 degree or pi
2cosX (1+cosX)=0
ie: 2cosX=0 or 1+cosX=0
Ans: X=90 degree or (pi)/2 or X= 180 degree or pi
收錄日期: 2021-04-13 15:24:47
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080410000051KK00806