數學...............
回答 (2)
2007-05-14 3:10 am
✔ 最佳答案
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2007-05-13 19:13:33 補充：
參考資料：http://mathworld.wolfram.com/SecondDerivativeTest.html
2007-05-14 2:20 am
應該係x和y都為0時
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https://hk.answers.yahoo.com/question/index?qid=20070513000051KK03777