[微積] x加x次以後的微分
有個問題是這樣的:
2+2 = 2^2
3+3+3 = 3^2
4+4+4+4 = 4^2
.
.
.
x+x+...+x = x^2 (加了x次)
現在左右兩邊各自作導函數
等號左邊是1+1+...+1=x (1連加x次)、右邊是2x,但左右兩邊並不相等,請解釋。
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我的解釋是這樣的,設x的整數部分叫h(x)、小數部分叫g(x),
所以x^2 = xh(x)+xg(x)
等號右邊作導函數為h+xh'+g+xg' = (h+g) + x(h'+g') = x + x =2x,與等號左邊
取導函數的答案相同。
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也不知道這樣想有沒有問題,但我更希望以線代的向量空間去解釋,這樣能解釋成
因為變數x雖然連加了x次,每一項都是在同一個維度,這樣做會違反線性組合的微
分原則,所以同一維度的變數該先做完合併項以後才能做微分。
這樣想法有什麼問題嗎??
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