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Find the Taylor series at \(x=0\) for the given function, either by using the definition or by manipulating a known series. $$ f(x)=e^{x}-e^{-x} $$

Short Answer

Expert verified
The Taylor series for \( f(x) = e^x - e^{-x} \) at \(x=0\) is: \[ f(x) = 2 \sum_{n=0}^{\infty} \frac{x^{2n+1}}{(2n+1)!} \].

Step by step solution

01

- Understand the function

The given function is defined as: \[ f(x) = e^{x} - e^{-x} \]. This is a good candidate to use Taylor series because it involves exponential functions.
02

- Recall the Taylor series definition

The Taylor series for a function \(f(x)\) around \(x=0\) is given by: \[ f(x) = \sum_{n=0}^{\infty} \frac{f^{(n)}(0)}{n!} x^{n} \].
03

- Compute the derivatives

To find the coefficients for the Taylor series, compute the derivatives of \(f(x)\) at \(x=0\). \( f(x) = e^x - e^{-x} \) \( f'(x) = e^x + e^{-x} \) \( f''(x) = e^{x} - e^{-x} \) Continue taking derivatives until a pattern is noted.
04

- Evaluate derivatives at \(x=0\)

Evaluate the first few derivatives at \(x=0\): \( f(0) = e^0 - e^0 = 0 \) \( f'(0) = e^0 + e^0 = 2 \) \( f''(0) = e^0 - e^0 = 0 \) \( f'''(0) = e^0 + e^{-0} = 2 \) \( f^{(4)}(0) = e^{0} - e^{-0} = 0 \) Notice the pattern: odd derivatives are 2, even derivatives are 0.
05

- Construct the Taylor series

Using the pattern identified in the derivatives, the Taylor series is: \[ f(x) = \sum_{n=0, n \text{ is odd}}^{\infty} \frac{2}{n!} x^{n} \]. Simplifying, we only have the odd terms: \[ f(x) = 2 \left( \frac{x}{1!} + \frac{x^3}{3!} + \frac{x^5}{5!} + \dots \right) \].
06

- Finalize the series

The Taylor series for \( f(x) = e^x - e^{-x} \) at \(x=0\) is: \[ f(x) = 2 \sum_{n=0}^{\infty} \frac{x^{2n+1}}{(2n+1)!} \].

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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 way to represent functions as an infinite sum of terms, calculated from the values of their derivatives at a single point. The general form for the Taylor series of a function \( f(x) \) around \( x=0 \) (also known as the Maclaurin series) is given by: \[ f(x) = \sum_{n=0}^{\infty} \frac{f^{(n)}(0)}{n!} x^{n} \].
Here, \( f^{(n)}(0) \) is the \( n \)-th derivative of \( f(x) \) evaluated at \( x=0 \), and \( n! \) denotes the factorial of \( n \).
This series is very useful because many functions that are difficult to deal with otherwise can be approximated by a simpler polynomial series.
In practice, we often use the first few terms of the Taylor series to approximate the function around a particular point.
exponential functions
Exponential functions are of the form \( e^x \), where \( e \) is the base of the natural logarithms, approximately equal to 2.71828.
These functions grow very quickly and have unique properties, such as the rate of growth being proportional to the value of the function.
The Taylor series for the exponential function \( e^x \) around \( x=0 \) can be written as: \[ e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!} \].
This series converges for all values of \( x \), which makes it a powerful tool for approximations.
In the context of the given problem, we are dealing with the function \( f(x) = e^{x} - e^{-x} \). This function combines two exponential functions, one positive and one negative.
derivatives
A derivative represents the rate at which a function is changing at any given point.
For a function \( f(x) \), the first derivative \( f'(x) \) represents the slope of the function at point \( x \).
Higher-order derivatives (like the second derivative \( f''(x) \), third derivative \( f'''(x) \), and so on) provide more information about the curvature and the changing rates of the function.
In Taylor series, to find the coefficients of each term in the series, we compute multiple derivatives of the function up to the desired degree and evaluate them at \( x=0 \).
For the given function \( f(x) = e^x - e^{-x} \), here are the calculated derivatives: \[ f'(x) = e^x + e^{-x} \] \[ f''(x) = e^x - e^{-x} \] \[ f'''(x) = e^x + e^{-x} \] and so on.
When evaluating these derivatives at \( x=0 \), we notice a pattern where the odd derivatives are 2, and the even derivatives are 0. This pattern helps us construct the series efficiently.

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Most popular questions from this chapter

Determine whether the given geometric series converges or diverges. If the series converges, find its sum. $$ \sum_{n=0}^{\infty} e^{-0.5 n} $$

An investment guarantees annual payments of \(\$ 5,000\) in perpetuity, with the payments beginning immediately. Find the present value of this investment if the prevailing annual interest rate remains fixed at \(5 \%\) compounded continuously.

Economists refer to the process of moving from one job to another as labor migration. Such movement is usually undertaken as a means for social or economic improvement, but it also involves costs, such as the loss of seniority in the old job and the psychological cost of disrupting relationships. Consider the function \(^{+}\) $$ V=\sum_{n=1}^{N} \frac{E_{2}(n)-E_{1}(n)}{(1+i)^{n}}-\sum_{n=1}^{N} \frac{C_{m}(n)}{(1+i)^{n}}-C_{p} $$ \({ }^{*} \mathrm{C} . \mathrm{C} . \mathrm{Li}\), Human Genetics: Principles and Methods, New York: McGraw-Hill. 'G. K. Zipf, Human Behavior and the Principle of Least Effort, Cambridge, MA: Addison-Wesley. Another good source is C. E. Shannon and W. Weaver, The Mathematical Theory of Communication, Urbana, IL: Univ. of Illinois Press. \({ }^{2} \mathrm{C}\). R. McConnell and S. L. Brue, Contemporary Labor Economics, New York: MoGraw-Hill, 1992, pp. 440-444. where \(E_{2}(n)\) and \(E_{1}(n)\) denote the earnings from the new and old jobs, respectively, in year \(n\) after the move is to be made; \(i\) is the prevailing annual interest rate (in decimal form); \(N\) is the number of years the person is expected to be on the new job; and \(C_{m}\) and \(C_{p}\) are the expected monetary and net psychological costs of the move (psychological gain minus psychological loss). a. What does \(V\) represent? Why is the job move desirable if \(V>0\) and undesirable if \(V<0\) ? b. For simplicity, assume that \(E_{2}-E_{1}\) and \(C_{m}\) are constant for all \(n\) and that the person expects to stay on the new job "forever" once he or she moves (that is, \(N \rightarrow \infty\) ). Find a formula for \(V\), and use it to obtain a criterion for whether or not the job move should be made. [Hint: Your criterion should be an inequality involving \(E_{1}, E_{2}, C_{m}, C_{p}\), and \(i\).] c. Read an article on job mobility and labor migration, and write a paragraph on mathematical methods for modeling such issues.

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A developing country currently has 2,500 trained scientists. The government estimates that each year, \(6 \%\) of the current number of scientists either retire, die, or emigrate, while 278 new scientists graduate from college. If these trends continue, how many scientists will there be in 20 years? How many in the long run?

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