16.7k views
1 vote
Find a power series representation of the following function and determine the radius of convergence:

f(x) = x/(5 + x^2)
(A) Σ(-1)^n * x^(2n) / 5^n, R = 2

1 Answer

6 votes

Final answer:

The power series representation of the function f(x) is Σ(-1)^n * x^(2n+1) / 5^(n+1), and the radius of convergence (R) is √5. The coefficient and the exponent in the series expansion are adjusted in accordance with the geometric series formula and the function structure.

Step-by-step explanation:

A student has asked for the power series representation of the function f(x) = x/(5 + x^2) and the determination of the radius of convergence of that series. To find this power series representation, we can use the geometric series formula which is:

1/(1 - r) = Σr^n from n=0 to n=∞, where |r| < 1.

First, we rewrite the function in a form that allows us to use the geometric series:

f(x) = x/5 * 1/(1 + (x^2/5)) = (1/5)x * Σ(-1)^n * (x^2/5)^n

Now, we can write the power series expansion by distributing x and simplifying:

f(x) = Σ(-1)^n * x^(2n+1) / 5^(n+1), for |x^2/5| < 1

The radius of convergence (R) can be found by the inequality |x^2/5| < 1. Solving for |x|, we get |x| < √5, which means the radius of convergence is √5.

Therefore, the accurate power series representation of f(x) is Σ(-1)^n * x^(2n+1) / 5^(n+1), and the radius of convergence is √5, not 2 as indicated in the question.

User OnklMaps
by
8.7k points
Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories