Ch. 2 - Limits and Continuity

Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook

Hass 15th Edition

Ch. 2 - Limits and Continuity

Problem 2.46

Chapter 2, Problem 2.46

Limits and Infinity

Find the limits in Exercises 37–46.

x²/³ + x⁻¹
lim --------------------
x→∞ x²/³ + cos²x

Verified step by step guidance

First, identify the dominant terms in the numerator and the denominator as x approaches infinity. In this case, the dominant term in both the numerator and the denominator is x^(2/3).

Rewrite the expression by factoring out x^(2/3) from both the numerator and the denominator. This will help simplify the limit. The expression becomes: (x^(2/3) * (1 + x^(-5/3))) / (x^(2/3) * (1 + cos^2(x)/x^(2/3))).

Cancel out the common factor of x^(2/3) from the numerator and the denominator. This simplifies the expression to: (1 + x^(-5/3)) / (1 + cos^2(x)/x^(2/3)).

Evaluate the limit of each term as x approaches infinity. The term x^(-5/3) approaches 0, and cos^2(x)/x^(2/3) also approaches 0 because cos^2(x) is bounded between 0 and 1.

Substitute these limits into the simplified expression: (1 + 0) / (1 + 0) = 1. Therefore, the limit of the original expression as x approaches infinity is 1.

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Key Concepts

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

Limits

Limits are fundamental in calculus, representing the value that a function approaches as the input approaches a certain point. They are essential for understanding continuity, derivatives, and integrals. In this context, we are interested in the limit of a function as x approaches infinity, which helps determine the behavior of the function at extreme values.

Dominant Terms

In limit problems, especially as x approaches infinity, the dominant term in a polynomial or rational function significantly influences the limit's value. For example, in the expression x²/³ + x⁻¹, as x becomes very large, the term x²/³ will dominate over x⁻¹, allowing us to simplify the limit calculation by focusing on the leading term.

Trigonometric Functions and Limits

Trigonometric functions, such as cos²x, oscillate between fixed values, which can affect the limit of a function. In this case, as x approaches infinity, cos²x remains bounded between 0 and 1, meaning its contribution to the limit can be considered negligible compared to polynomial terms. Understanding how these functions behave at infinity is crucial for evaluating limits involving them.

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Related Practice

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Textbook Question

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a. It can be shown that the inequalities 1 − x²/ 6 < (x sin x) / (2−2cos x) < 1 hold for all values of x close to zero (except for x = 0). What, if anything, does this tell you about limx→0 (x sin x) / (2 − 2cos x)?

Give reasons for your answer.

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Textbook Question

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