Making sense of this formula relating to polynomials : P(x+n+1)=sum ni=0(−1)n−1(n+1i)P(x+i)

oliadas73

oliadas73

Answered question

2022-10-09

Making sense of this formula relating to polynomials :
P ( x + n + 1 ) = i = 0 n ( 1 ) n 1 ( n + 1 i ) P ( x + i )

Answer & Explanation

lascosasdeali3v

lascosasdeali3v

Beginner2022-10-10Added 10 answers

"If you take the right side over to the left (correcting a minor typo - ""n-1"" should be ""n-i"" in the power of -1), the equation can also be written like this:
i = 0 n + 1 1 n + 1 i n + 1 i P x + i = 0
What this is, is actually the iterated difference. That is, if Δ f 0 = f 1 f 0 , and Δ 2 f 0 = Δ f 1 f 0 = f 2 2 f 1 + f 0 Δ n + 1 P x = 0
And if our polynomial is of order n or lower, then this must be true. To see this, consider that, for P x = x n , we have
Δ x n = x + 1 n x n = k = 0 n 1 n k x k
And
Δ C = 0
for any constant C. So, iterating the Δ operation n + 1 times, you end up with Δ n + 1 x n = 0"

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