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Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.

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Statement

Notation as on the Statement (I) page: pnp_n and qnq_n are the normalized polynomials (1) and (2) of degrees 2n+12n+1 and 2n+22n+2 with zeros at consecutive integers.

Statement (II) (p. 294). For 0<x<n0<x<n with xx not an integer,

∣pn+1(x)∣>(n+1) ∣qn(x)∣>(n+1) ∣pn(x)∣.(4)|p_{n+1}(x)|>(n+1)\,|q_n(x)|>(n+1)\,|p_n(x)|. \tag{4}

Hence, in the system (1)--(2), increasing the degree increases both the area and the maximum of the absolute value of the polynomial on each fixed arch.

Unlike Statement (I), this monotonicity depends on the coordinate scale fixed by (1) and (2), as the paper notes (p. 294).

Read depth. Claims checked: the statement was read clause by clause on the page image of p. 294. The short proof was followed.

Proof pointer

P. 294. The factorization pn+1(x)=(x+n+1) qn(x)=(x+n+1)(x−n−1) pn(x)p_{n+1}(x)=(x+n+1)\,q_n(x)=(x+n+1)(x-n-1)\,p_n(x) and, for 0<x<n0<x<n, the bounds ∣x+n+1∣>n+1|x+n+1|>n+1 and ∣x−n−1∣=n+1−x>1|x-n-1|=n+1-x>1.

Dependencies

None beyond the definitions (1) and (2).

Bears on

None recorded. The paper presents the analogue of (II) for the zeros of the derivative as relations (7)--(11).