TheoremBase

The Exponential Function Dominates Every Polynomial Function

Statement

Let R\mathbb{R} be the real numbers, an ordered field with order ≤\le, write ∣t∣|t| for the absolute value of t∈Rt\in\mathbb{R} and t−1t^{-1} for the multiplicative inverse of t≠0t\ne 0, and let exp⁡\exp be the exponential function. Let pp be a polynomial function on R\mathbb{R}.

Then the following hold.

1. (Decay at +∞+\infty) For every ε∈R\varepsilon\in\mathbb{R} with 0<ε0<\varepsilon there is M∈RM\in\mathbb{R} with 1≤M1\le M such that

∣p(t)∣exp⁡(−t)<εfor every t∈R with M≤t.|p(t)|\exp(-t)<\varepsilon\qquad\text{for every }t\in\mathbb{R}\text{ with }M\le t.

2. (Decay at 00 from the right) For every ε∈R\varepsilon\in\mathbb{R} with 0<ε0<\varepsilon there is δ∈R\delta\in\mathbb{R} with 0<δ0<\delta such that

∣p(s−1)∣exp⁡(−s−1)<εfor every s∈R with 0<s<δ.\bigl|p\bigl(s^{-1}\bigr)\bigr|\exp\bigl(-s^{-1}\bigr)<\varepsilon\qquad\text{for every }s\in\mathbb{R}\text{ with }0<s<\delta.

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