Math Problem Statement

f(x) = 5/(1-x^6) find the power series representation and interval of convergence

Solution

To find the power series representation of the function f(x)=51x6f(x) = \frac{5}{1 - x^6} and determine its interval of convergence, let's proceed step-by-step.

Step 1: Rewrite the Function

We can express f(x)f(x) in a form that resembles a geometric series. Notice that: f(x)=51x6f(x) = \frac{5}{1 - x^6} This can be written as: f(x)=511x6f(x) = 5 \cdot \frac{1}{1 - x^6}

Step 2: Apply the Geometric Series Expansion

The standard geometric series expansion is: 11u=n=0unforu<1\frac{1}{1 - u} = \sum_{n=0}^{\infty} u^n \quad \text{for} \quad |u| < 1 Here, we set u=x6u = x^6. Then: 11x6=n=0(x6)n=n=0x6n\frac{1}{1 - x^6} = \sum_{n=0}^{\infty} (x^6)^n = \sum_{n=0}^{\infty} x^{6n} Thus, we can write: f(x)=5n=0x6n=n=05x6nf(x) = 5 \cdot \sum_{n=0}^{\infty} x^{6n} = \sum_{n=0}^{\infty} 5 x^{6n}

Step 3: Determine the Interval of Convergence

The power series n=0x6n\sum_{n=0}^{\infty} x^{6n} converges when x6<1|x^6| < 1, which simplifies to: x<1|x| < 1 Therefore, the interval of convergence for this series is: x<1|x| < 1 or in interval notation: (1,1)(-1, 1)

Final Answer

The power series representation of f(x)f(x) is: f(x)=n=05x6nf(x) = \sum_{n=0}^{\infty} 5 x^{6n} with an interval of convergence x<1|x| < 1 (or (1,1)(-1, 1)).

Would you like more details on any part of this solution?

Here are some related questions:

  1. How would you find the radius of convergence of a general power series?
  2. Can this approach be extended to functions with different exponents in the denominator?
  3. How does the geometric series formula help in finding power series representations?
  4. What happens to the power series if the function had a different constant, say 101x6\frac{10}{1 - x^6}?
  5. How does the interval of convergence change if the exponent inside is x4x^4 instead of x6x^6?

Tip: When working with power series, always verify the form against the geometric series for easy expansion.

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Math Problem Analysis

Mathematical Concepts

Power Series
Geometric Series
Interval of Convergence
Algebra

Formulas

Geometric Series Expansion: 1/(1 - u) = sum(u^n) for |u| < 1
Power Series Representation: f(x) = sum(a_n * x^n)

Theorems

Geometric Series Convergence Theorem

Suitable Grade Level

Grades 11-12