~~Polynomial 與 Differentiation~~

2007-02-24 2:22 am
I recently think about the following statement:
‘For polynomial P and integer n ≧ deg(P)+1, dⁿ/dⁿx(P) = 0.’
Is that correct?
If yes, please give a proof. If no, please give a negative example.

回答 (2)

2007-02-24 2:58 am
✔ 最佳答案
Obviously, it is correct.

      m      m-1          0
P=(a x )+(a x   )+ … +(a x ) .... (1)
    0      1            m

Differentiate (1) by m times with respect to x,

                0
[d^m / (dx)^m] (P) = m!(a x )+0+0+ … +0
              0

        = m!a ....................... (2)
             0

Further differentiate (2) once with respect to x,
[d^(m+1) / (dx)^(m+1)] (P) = 0

Differentiating 0 further will only give 0.

So, differentiating (1) for n times with respect to x, where n≧m+1, gives 0.
2007-03-12 5:50 am
This is a correct answer.


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