Power Series Representation of xln(1+x^2)

In summary, to write a power series representation of xln(1+x2), you can expand ln(1+x^2) around x=0 since the power series expansion of x is x. The power series expansion of ln(1+u) around u=0 is ln(1+u) = u - u^2/2 + u^3/3 - ... . Therefore, the power series expansion of ln(1+x^2) is ln(1+x^2) = x^2 - x^4/2 + x^6/3 - ... . There is no need to worry about a double summation.
  • #1
PCSL
146
0
Write a power series representation of xln(1+x2)

My first instinct was to attempt to take the second derivative and then find the summation and then integrate but that approach seemed to be a dead end. Basically, the x thrown in there confuses me and you can't split the function into two separate summations since one would not converge. Any hints..?
 
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  • #2
Help, anyone?
 
  • #3
I assume you are expanding around x=0. The power series expansion of x is x. What's the power series expansion of ln(1+u) around u=0? Hence what's the power series expansion of ln(1+x^2). There is no double summation to worry about.
 
  • #4
Dick said:
I assume you are expanding around x=0. The power series expansion of x is x. What's the power series expansion of ln(1+u) around u=0? Hence what's the power series expansion of ln(1+x^2). There is no double summation to worry about.

I really need to put more thought into problems before posting here. Thanks, and I figured it out.
 

1. What is a power series representation?

A power series representation is a way of expressing a function as an infinite sum of terms, with each term being a constant multiple of a power of the independent variable.

2. How is xln(1+x^2) represented as a power series?

The power series representation of xln(1+x^2) is ∑n=0∞ ((-1)^n * x^(2n+1))/(2n+1), where n is a non-negative integer.

3. Why is the power series representation of xln(1+x^2) useful?

The power series representation of xln(1+x^2) can be used to approximate the value of the function for any value of x, as well as to calculate the derivatives and integrals of the function.

4. How is the accuracy of the power series representation determined?

The accuracy of the power series representation depends on the convergence of the series. The series will converge for values of x within a certain interval, and the closer the value of x is to the center of this interval, the more accurate the representation will be.

5. Can the power series representation be used for other functions?

Yes, the power series representation can be used for a wide range of functions, including polynomial, exponential, trigonometric, and logarithmic functions. It is a powerful tool in mathematics and science for approximating and analyzing functions.

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