Skip to main content
Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.8.10.a

10. True, or false? As x→∞,
a. 1/(x+3) = O(1/x)

Verified step by step guidance
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 \(x_0\) such that for all \(x > x_0\), \(|f(x)| \leq C |g(x)|\).
Identify the functions in the problem: \(f(x) = \frac{1}{x+3}\) and \(g(x) = \frac{1}{x}\).
Compare the behavior of \(f(x)\) and \(g(x)\) as \(x \to \infty\). Notice that \(\frac{1}{x+3}\) behaves very similarly to \(\frac{1}{x}\) because adding 3 becomes insignificant for very large \(x\).
To verify the Big-O relationship, consider the ratio \(\frac{|f(x)|}{|g(x)|} = \frac{\frac{1}{x+3}}{\frac{1}{x}} = \frac{x}{x+3}\). As \(x \to \infty\), this ratio approaches 1, which is a finite constant.
Since the ratio approaches a finite constant, there exist constants \(C\) and \(x_0\) such that \(|f(x)| \leq C |g(x)|\) for all \(x > x_0\), confirming that \(\frac{1}{x+3} = O\left(\frac{1}{x}\right)\) is true.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

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, focusing on its behavior as the input approaches infinity. It provides a way to classify functions according to their dominant terms, ignoring constant factors and lower-order terms.
Recommended video:
04:22
Sigma Notation

Asymptotic Behavior of Functions

Asymptotic behavior studies how functions behave as the input variable grows very large. Understanding limits and dominant terms helps compare functions like 1/(x+3) and 1/x as x approaches infinity.
Recommended video:
5:50
Asymptotes of Hyperbolas

Equivalence of Functions in Big O Terms

Two functions f(x) and g(x) are related by f(x) = O(g(x)) if there exist constants C and x0 such that |f(x)| ≤ C|g(x)| for all x > x0. This means f(x) grows no faster than a constant multiple of g(x) for large x.
Recommended video:
7:30
Logarithms Introduction