amaths
回答 (1)
2008-02-19 1:36 am
✔ 最佳答案
2sinxsin3x=1 -cos(x+3x)+cos(x-3x)=1
-cos4x+cos2x=1
-2cos²2x+1+cos2x=1
cos2x(1-2cos2x)=0
cos2x=0 or cos2x=1/2
2x=2nπ±π/4 or 2x=2nπ±π/3
x=nπ±π/8 or x=nπ±π/6
收錄日期: 2021-04-23 20:33:29
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080218000051KK01929