Chapter 9: Problem 36
Use series to evaluate the limits. $$\lim _{x \rightarrow \infty}(x+1) \sin \frac{1}{x+1}$$
Short Answer
Expert verified
The limit is 1.
Step by step solution
01
Rewrite Using the Series Expansion
The expression involves \(\sin \frac{1}{x+1}\), which can be expanded using the Taylor series for sine. Recall that the Taylor series for \(\sin u\) is \(u - \frac{u^3}{3!} + \frac{u^5}{5!} - \cdots\). For very large \(x\), this becomes:\[\sin \frac{1}{x+1} \approx \frac{1}{x+1}\].
02
Simplify the Expression
Substituting the series expansion into the original limit gives us:\[\lim_{x \to \infty} (x+1) \sin \frac{1}{x+1} \approx \lim_{x \to \infty} (x+1) \left( \frac{1}{x+1} \right) = \lim_{x \to \infty} 1\].
03
Evaluate the Limit
Since the expression simplifies to \(1\), the limit becomes:\[\lim_{x \to \infty} 1 = 1\]. The result shows that as \(x\) approaches infinity, the original expression approaches 1.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Taylor Series
The Taylor series is a mathematical tool used to express functions as infinite sums of terms calculated from the values of their derivatives at a single point. It acts like a "recipe" to approximate more complex functions by a polynomial, making them easier to analyze or compute.
- The formula for a Taylor series about zero (also known as a Maclaurin series) for a function \( f(x) \) is expressed as:
- For the sine function, \( \sin(u) \), the series becomes \( u - \frac{u^3}{3!} + \frac{u^5}{5!} - \cdots \).
- This is particularly useful when \( u \) is small, allowing higher-order terms to become negligible, simplifying calculations.
Sine Function
The sine function, noted as \( \sin(x) \), is a fundamental trigonometric function known for its wave-like pattern.
- Its values oscillate between -1 and 1, making it periodic with a period of \( 2\pi \).
- Key properties include its symmetry and its odd function characteristic: \( \sin(-x) = -\sin(x) \).
- Hence, \( \sin(\frac{1}{x+1}) \approx \frac{1}{x+1} \) when \( x \) is large.
- This approximation is crucial when evaluating limits, as it simplifies the terms involved.
Limit Evaluation
Limit evaluation is a method used to determine the behavior of a function as its input approaches a particular value. This is integral in calculus and helps to solve indeterminate forms or to evaluate the behavior of functions at boundaries.
- One relies on algebraic manipulation, L'Hôpital's rule, or series expansion to resolve these limits.
- The expression \( \lim_{x \to \infty} (x+1) \sin(\frac{1}{x+1}) \) transforms into \( \lim_{x \to \infty} 1 \).
- This simplification was possible because the product \( (x+1)\frac{1}{x+1} \) intuitively resolves to 1 as \( x \) approaches infinity.