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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.P.112a

112. True, or false? Give reasons for your answers.
a. 1/x⁴ = O(1/x² + 1/x⁴)

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1
Recall the definition of Big-O notation: A function \(f(x)\) is \(O(g(x))\) as \(x \to \infty\) if there exist positive constants \(C\) and \(M\) such that for all \(x > M\), \(|f(x)| \leq C |g(x)|\).
Identify the functions involved: \(f(x) = \frac{1}{x^4}\) and \(g(x) = \frac{1}{x^2} + \frac{1}{x^4}\).
Analyze the behavior of \(g(x)\) as \(x \to \infty\): Since \(\frac{1}{x^2}\) dominates \(\frac{1}{x^4}\) for large \(x\), \(g(x)\) behaves roughly like \(\frac{1}{x^2}\).
Compare \(f(x)\) and \(g(x)\): For large \(x\), \(\frac{1}{x^4}\) is smaller than or equal to a constant multiple of \(\frac{1}{x^2}\), so \(f(x)\) is bounded above by \(g(x)\) times some constant.
Conclude whether \(f(x) = O(g(x))\) holds by verifying if the inequality \(|f(x)| \leq C |g(x)|\) can be satisfied for some constants \(C\) and \(M\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Big O Notation

Big O notation describes the upper bound of a function's growth rate, showing how it behaves as the input approaches a limit, often infinity. It helps compare functions by their dominant terms, ignoring lower-order terms and constants.
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Asymptotic Comparison of Functions

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Properties of Rational Functions

Rational functions are ratios of polynomials. Understanding their behavior, especially for terms like 1/x² and 1/x⁴, is crucial to analyze limits and growth rates, as higher powers in the denominator lead to faster decay as x increases.
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