Is f(x) Representable as a Special Function?

In summary, the conversation discusses the function f(x) and its representation as an elementary or defined special function. It is then broken up into two expressions and simplified to equal -1/(1+x^2). It is noted that this is a geometric series with a ratio of -1/x^2.
  • #1
pierce15
315
2
Hi, does anyone know if this function:

[tex] f(x) = \sum_{k=1}^\infty \frac{(-1)^n}{x^{2k}} [/tex]

is representable as an elementary or already defined special function? Thanks
 
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  • #2
This function can be broken up as:

[tex] f(x) = \sum_{k=1}^\infty x^{4k} - \sum_{n=1}^\infty x^{4n-2} [/tex]

Any ideas?
 
  • #3
I think I've got it: the above expression is equal to

[tex] \frac{1}{x^4 - 1} - \frac{ x^2} {x^4 - 1} = - \frac{1}{1 + x^2} [/tex]

does that look ok?
 
  • #4
piercebeatz said:
I think I've got it: the above expression is equal to

[tex] \frac{1}{x^4 - 1} - \frac{ x^2} {x^4 - 1} = - \frac{1}{1 + x^2} [/tex]

does that look ok?

Answer is correct. It is a geometric series, ratio = -1/x2.
 
  • #5
Oh, right. I'm an idiot for not seeing that to begin with
 

FAQ: Is f(x) Representable as a Special Function?

What is a function defined as a series?

A function defined as a series is a mathematical concept where a function can be represented as an infinite sum of simpler functions, known as a series. This means that the function's output can be calculated by adding up the values of the simpler functions at different input values.

How is a function defined as a series different from a regular function?

In a regular function, the output can be calculated directly from the input using a specific formula or set of rules. In a function defined as a series, the output is calculated by adding up the values of simpler functions, making it more complex and requiring an infinite number of terms to accurately represent the function.

What is the importance of functions defined as series in mathematics?

Functions defined as series are important in mathematics because they allow for the representation of complex functions that may not have a simple formula. They also have applications in calculus, where they are used to approximate functions and solve problems involving infinite sums.

Can any function be represented as a series?

No, not all functions can be represented as a series. This is because some functions may not have an infinite sum of simpler functions that accurately represents them. Functions that do not have a series representation are known as non-analytic functions.

How are functions defined as series used in real-world applications?

Functions defined as series have various real-world applications, such as in physics, engineering, and economics. They are used to model complex systems and make predictions based on the input data. In finance, series functions are used to calculate interest rates and investment returns. In physics, they are used to model the behavior of waves and electromagnetic fields.

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