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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
All textbooksHass 15th EditionCh. 7 - Transcendental FunctionsProblem 7.8.17
Chapter 7, Problem 7.8.17

17. Show that √(10x+1) and √(x+1) grow at the same rate as x→∞ by showing that they both grow at the same rate as √x as x→∞.

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Identify the functions given: \( f(x) = \sqrt{10x + 1} \) and \( g(x) = \sqrt{x + 1} \). We want to compare their growth rates as \( x \to \infty \).
Recall that to show two functions grow at the same rate as \( x \to \infty \), we can compare their ratios to a common function that represents the growth rate. Here, the common function is \( h(x) = \sqrt{x} \).
Compute the limit of the ratio \( \frac{f(x)}{h(x)} = \frac{\sqrt{10x + 1}}{\sqrt{x}} \) as \( x \to \infty \). Simplify the expression inside the limit by factoring out \( x \) inside the square root in the numerator.
Similarly, compute the limit of the ratio \( \frac{g(x)}{h(x)} = \frac{\sqrt{x + 1}}{\sqrt{x}} \) as \( x \to \infty \). Simplify this expression by factoring out \( x \) inside the square root in the numerator.
Evaluate both limits to find finite, nonzero constants. Since both limits exist and are finite and nonzero, conclude that \( f(x) \) and \( g(x) \) grow at the same rate as \( h(x) = \sqrt{x} \) as \( x \to \infty \), and therefore \( f(x) \) and \( g(x) \) grow at the same rate as each other.

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Key Concepts

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

Asymptotic Growth and Limits

Asymptotic growth describes how functions behave as the input grows very large. Using limits, we compare the ratio of two functions as x approaches infinity to determine if they grow at the same rate. If the limit of their ratio is a finite nonzero constant, the functions have the same growth rate.
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Square Root Function Behavior

The square root function, √x, grows slower than linear functions but faster than logarithmic ones. Understanding how expressions like √(10x+1) and √(x+1) relate to √x helps in comparing their growth rates by factoring out √x and analyzing the remaining terms as x becomes large.
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Limit of a Ratio to Compare Growth Rates

To show two functions grow at the same rate, we examine the limit of their ratio as x approaches infinity. For example, evaluating lim(x→∞) √(10x+1)/√x simplifies to √10, a finite constant, indicating both functions grow proportionally to √x and thus at the same rate.
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