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![](https://cache.ptt.cc/c/https/i.imgur.com/5PyJG6sl.jpg?e=1665052028&s=SABBigSq8e9zP1B_ndaJ5g)
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※ 文章網址: https://www.ptt.cc/bbs/Examination/M.1445773639.A.E10.html
推 loveyou999: http://i.imgur.com/5PyJG6s.jpg10/25 20:48
推 loveyou999: http://i.imgur.com/K7ibw9z.jpg10/25 20:50
→ loveyou999: Sin,Cos間的轉換可用做圖法來看較簡單喔~ 逆時針角10/25 20:52
→ loveyou999: 度為正,順時針為負10/25 20:52
推 loveyou999: 另外你所問的~應該是Cos(2a+90)=-Sin(2a)…你把2a略10/25 21:39
→ loveyou999: 掉了10/25 21:39
→ x014067: 你也可以展開cos(A+B)=cosAcosB-sinAsinB,負號從這來的10/25 22:11