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作者 jacky7987 在 PTT [ Math ] 看板的留言(推文), 共3105則
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2F推: arctan(x)+arccot(x)= pi/2 , 然後arctan是奇函數09/30 17:06
3F→: 但好像差個x *pi/2 大概有個是錯的吧09/30 17:06
1F推: 比方說是熱方程,(∂_t-Δ)u=0, 你可以把前面的微分09/08 15:59
2F→: 看成一個從C^inf(R^n x (0,inf] )送到R的算子09/08 16:00
3F→: 前者維度是無窮維度的啦,所以你也很難寫等式09/08 16:01
4F→: 而你的解掉在那個算子的kernel裡面09/08 16:01
1F推: 1. 我沒看到f的圖不知道怎麽回答08/25 17:34
2F→: 2. 做兩次integration by part就會得到08/25 17:34
4F推: 你對int e^t sin(wt) dt做兩次integration by part08/27 15:52
5F→: 會得到一個 int e^t sin(wt) dt 的代數方程08/27 15:52
6F→: 喔喔H大已經回了08/27 15:54
7F→: 1. 的話就可能f就是e^{-t}吧08/27 15:54
3F推: 有n^2跟未知數,n條方程式。有解的話有辦法,只是08/20 13:49
4F→: 解不會唯一08/20 13:49
1F推: 他應該是展 1/(1-x)=sum x^n, 再對兩邊微分,然後08/01 18:50
2F→: 再把x換成2/sqrt{x}08/01 18:51
3F→: C(r, k) 就直接訂成r*...(r-k+1)/k!08/01 18:55
4F→: 這兩個應該是一樣才對(但是我懶得算,給你算08/01 18:56
2F推: 反正都是有限維,你就想成 R^n x R^m07/03 14:47
1F推: 是07/01 21:45
1F推: 這樣寫不是太好。首先因為ker 跟 Im不是同一個V07/01 16:11
2F→: 所以頂多是同構,再來就是那句話並沒有很直接推07/01 16:12
3F→: 論到你的結論。我不確定你要證明的是什麼,如果單就07/01 16:12
4F→: 那句話是對的吧XD07/01 16:13
5F→: 好像也是可以寫等於,只是一瞬間會覺得乖乖的XDD07/01 16:14
6F→: 如果你單要證明最後一句話,應該是straightforward07/01 16:15
7F→: 證好像比較簡單,給v in V, take w=T(v), u=v-T(v)07/01 16:16
8F→: 好像不是這樣XDD 讓我想一下07/01 16:17
9F→: 抱歉整個想錯,好像隨便就可以造反例XDD07/01 16:21
10F→: T=[0 1;0 0], ker(T)=span([1;0])=Im(T)07/01 16:22
6F推: 因為第一句是錯的,所以第二句無論如何都是T07/01 16:08