Can You Help Me Find a Power Series?

In summary, the conversation is about finding the power series for the given expression and asking for hints and help. The formula for the power series is given, and there is a discussion about the use of factorials and the final solution is given as the exponential function.
  • #1
overseastar
25
0
Hi
I"m having truoble with fnding the power series of the following::frown:

1+(x^3)/3+(x^6)/18+(x^9)/162+...

Can anyone give me a hand?

Also, any hints in finding a power series?

Thanks !
 
Physics news on Phys.org
  • #2
That IS a power series...
 
  • #3
Hahaha... or did you mean, you have trouble putting it into compact [itex]\sum[/itex] notation?
 
  • #4
I am guessing that overseastar is looking for a closed form of the sum.
 
  • #5
Looks like:

[tex]\sum_{n=0}^{a}\frac{x^{3n}}{3^n3!}[/tex]
 
  • #6
Joffe said:
Looks like:

[tex]\sum_{n=0}^{a}\frac{x^{3n}}{3^n3!}[/tex]


Why do you use the factorial when 3 ! = 6 which is constant ?
 
  • #7
Joffe said:
Looks like:

[tex]\sum_{n=0}^{a}\frac{x^{3n}}{3^n3!}[/tex]
That fails to work when the denominator is 3.
 
  • #8
I think he means [tex]\sum_{n=0}^{\infty}\frac{x^{3n}}{3^nn!}[/tex]
 
  • #9
Thankyou Moo Of Doom, that is what I meant to write.
 
  • #10
And [tex]\sum_{n=0}^{\infty}\frac{x^{3n}}{3^nn!}[/tex]
is equal to
[tex]\sum_{n=0}^{\infty}\frac{1}{n!}\left(\frac{x^3}{3}\right)^n[/tex]
Anyone recognize THAT??
 
  • #11
No I don't, please enlighten me.
 
  • #12
[tex]\sum_{n=0}^{\infty}\frac{1}{n!}\left(\frac{x^3}{3}\right)^n=\exp{\left(\frac{x^3}{3}\right)}[/tex]
 
  • #13
oh wow, yes, that's what i meant, sorry
 
  • #14
And thank you for all your help !
 

What is a power series and why is it useful in science?

A power series is an infinite series of the form ∑ an(x-c)n, where a is a coefficient, x is the variable, and c is the center. It is useful in science because it can represent a wide variety of functions and can be used to approximate more complex functions. Power series are also used in calculus and mathematical analysis to solve differential equations and study the behavior of functions.

How do you find a power series for a given function?

To find a power series for a given function, you need to first determine the center of the series. This can be done by finding the value of x that makes the highest power of x equal to zero. Then, you can use the formula for a power series to find the coefficients, which involve taking derivatives of the function at the center. The result will be an infinite series that approximates the given function.

Can a power series represent any function?

No, a power series can only represent functions that are analytic, meaning they can be represented as an infinite sum of powers of x. Functions that have discontinuities, such as step functions, or functions that are not continuous, such as the absolute value function, cannot be represented by a power series.

How accurate is a power series approximation?

The accuracy of a power series approximation depends on the function and the number of terms used in the series. In general, the more terms included in the series, the more accurate the approximation will be. However, there may be cases where even an infinite number of terms will not give an exact representation of the function.

In what other fields besides mathematics is the concept of power series used?

Power series are used in many fields besides mathematics, including physics, engineering, and economics. In physics, power series are used to approximate physical phenomena such as electric fields and gravitational forces. In engineering, they are used to model systems and solve differential equations. In economics, power series are used to analyze trends and make predictions in financial markets.

Similar threads

  • Precalculus Mathematics Homework Help
Replies
13
Views
2K
  • Calculus and Beyond Homework Help
Replies
7
Views
704
  • Calculus and Beyond Homework Help
Replies
8
Views
1K
  • Calculus and Beyond Homework Help
Replies
1
Views
254
  • Calculus and Beyond Homework Help
Replies
4
Views
1K
Replies
1
Views
1K
  • Precalculus Mathematics Homework Help
Replies
2
Views
1K
  • Calculus and Beyond Homework Help
Replies
9
Views
2K
  • Differential Equations
Replies
8
Views
523
  • Calculus and Beyond Homework Help
Replies
3
Views
278
Back
Top