推 craig100 :平方 湊cos和角 09/23 02:04
→ oxs77 :嗯...請問 cosx^2- sinx^2 怎麼知道? 09/23 02:10
推 doa2 :1F這樣做只能做出cos(x-y)唷 09/23 02:14
推 craig100 :真的耶 囧!! 09/23 02:15
→ doa2 :應該是先用和差化積..相除求出tan[(x+y)/2]再求cos 09/23 02:15
→ craig100 :剛算一下 可以先求出cos(x-y) 然後換成相剪的話 09/23 02:17
→ craig100 :可得cos2x +cos2y +2cos(x+y)=5/36 09/23 02:17
→ craig100 :前面用和差化積 就可以做了 09/23 02:17
→ oxs77 :謝了~ 果然還是要用合差化積.. 09/23 02:19