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Ch. 2 - Limits
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 2.7.48

Use the precise definition of infinite limits to prove the following limits.


limx→0(1x4−sin(x))=∞{\(\displaystyle\[\lim\)_{x\(\to\)0}}\(\left\)(\(\frac{1}{x^4}\)-\(\sin\]\left\)(x\(\right\))\(\right\))=\(\infty\)

Guida verificata passo dopo passo
1
Step 1: Understand the definition of an infinite limit. The limit \( \lim_{x \to a} f(x) = \infty \) means that for every positive number \( M \), there exists a \( \delta > 0 \) such that if \( 0 < |x - a| < \delta \), then \( f(x) > M \).
Step 2: Consider the function \( f(x) = \frac{1}{x^4} - \sin(x) \). As \( x \to 0 \), \( \frac{1}{x^4} \to \infty \) and \( \sin(x) \to 0 \). Therefore, \( f(x) \to \infty \).
Step 3: For a given \( M > 0 \), we need to find \( \delta > 0 \) such that if \( 0 < |x| < \delta \), then \( \frac{1}{x^4} - \sin(x) > M \).
Step 4: Since \( \sin(x) \) is bounded, \( |\sin(x)| \leq |x| \). Therefore, \( \frac{1}{x^4} - \sin(x) \geq \frac{1}{x^4} - |x| \).
Step 5: Choose \( \delta \) small enough such that \( \frac{1}{x^4} - |x| > M \) for \( 0 < |x| < \delta \). This ensures that \( \frac{1}{x^4} - \sin(x) > M \), proving the limit is infinite.

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Infinite Limits

Infinite limits describe the behavior of a function as the input approaches a certain value, where the function's output grows without bound. Specifically, if the limit of a function as x approaches a value results in infinity, it indicates that the function increases indefinitely in that vicinity. Understanding infinite limits is crucial for analyzing functions that exhibit vertical asymptotes or unbounded growth.
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The sine function, denoted as sin(x), oscillates between -1 and 1 for all real numbers x. As x approaches 0, sin(x) can be approximated by its Taylor series expansion, which shows that sin(x) behaves like x near zero. This property is essential for evaluating limits involving sin(x) and understanding how it interacts with other functions, particularly in the context of limits approaching zero.
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The precise definition of a limit involves the concept of approaching a value as closely as desired. To prove limits, one often uses algebraic manipulation, substitution, or the epsilon-delta definition. In this case, evaluating the limit requires analyzing the expression as x approaches 0, particularly focusing on the dominant term in the expression, which is crucial for determining the limit's behavior.
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