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[微積] continuous derivative 問題

看板Math板作者anoymouse (沒有暱稱)
時間. (2024-03-21 16:37:52)
推文12則 (4推 0噓 8→)
Thomas' calculus 關於積分弧長,有先做一個前提:
Suppose the curve whose length we want to find is the graph of the function
y = f(x) from x= a to x = b.
In order to derive an integral formula for the length of the curve, we assume
that ƒ has a continuous derivative at every point of [a, b]. Such a function
is called smooth,and its graph is a smooth curve because it does not have any breaks, corners,
or cusps.

最後說到:
(1 + [f'(x)]^2)^1/2 is continuous on [a,b]


想問f has a continuous derivative ... of [a,b]的意思是
(1) f'(x) is continuous on [a,b] 還是
(2) f在[a,b]每一點都有derivative

如果是(2) 舉一個example https://imgur.com/Wv2wDLl
g(x)每一點都有derivative 但是 g'(0)在x = 0 並不連續。
這樣的話 "(1 + [f'(x)]^2)^1/2 is continuous " 就不一定會成立吧?

所以原文的意思是應該是(1)?
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#1
: 您po的原文敘述有強調是平滑曲線,排除斷點 折角03/21 18:46
#2              "not have any breaks, corners or cusps."03/21 18:47
#3
  : 所以你認為是(2)?03/21 20:33
#4              我的舉例g of x雖然靠近0會劇烈跳動 但應該每個點都03/21 20:33
#5              可以微分且g'在0不連續吧 這樣不符合圓滑曲線嗎03/21 20:33
#6
  : 這是英文問題不是數學問題,a continuous derivativ03/21 23:06
#7              e 的意思是 a derivative that is continuous 也就03/21 23:06
#8              是導數是一個連續函數。03/21 23:06
#9
    : 就 (1)03/21 23:12
#10
   : 我還以為是要問在端點微分是什麼意思XD03/22 04:19
#11
  : 好的 謝謝各位03/22 08:39
#12
: 當然是 1,語意蠻明確的03/22 11:05

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