Math Problem Statement

Use the definition of Taylor series to find the Taylor series (centered at c) for the function.

f(x) = ln(x), c = 1

Solution

To find the Taylor series of the function f(x)=ln(x)f(x) = \ln(x) centered at c=1c = 1, we use the Taylor series definition:

f(x)=f(c)+f(c)(xc)+f(c)2!(xc)2+f(c)3!(xc)3+f(x) = f(c) + f'(c)(x - c) + \frac{f''(c)}{2!}(x - c)^2 + \frac{f'''(c)}{3!}(x - c)^3 + \cdots

Step 1: Calculate the derivatives

  1. First derivative: f(x)=1xf'(x) = \frac{1}{x} Evaluating at c=1c = 1: f(1)=1f'(1) = 1

  2. Second derivative: f(x)=1x2f''(x) = -\frac{1}{x^2} Evaluating at c=1c = 1: f(1)=1f''(1) = -1

  3. Third derivative: f(x)=2x3f'''(x) = \frac{2}{x^3} Evaluating at c=1c = 1: f(1)=2f'''(1) = 2

  4. Fourth derivative: f(4)(x)=6x4f^{(4)}(x) = -\frac{6}{x^4} Evaluating at c=1c = 1: f(4)(1)=6f^{(4)}(1) = -6

  5. Fifth derivative: f(5)(x)=24x5f^{(5)}(x) = \frac{24}{x^5} Evaluating at c=1c = 1: f(5)(1)=24f^{(5)}(1) = 24

Step 2: Construct the Taylor series

Now, we can substitute these values into the Taylor series formula:

f(x)=ln(1)+1(x1)12(x1)2+26(x1)3624(x1)4+24120(x1)5+f(x) = \ln(1) + 1(x - 1) - \frac{1}{2}(x - 1)^2 + \frac{2}{6}(x - 1)^3 - \frac{6}{24}(x - 1)^4 + \frac{24}{120}(x - 1)^5 + \cdots

Since ln(1)=0\ln(1) = 0, we have:

f(x)=(x1)12(x1)2+13(x1)314(x1)4+15(x1)5+f(x) = (x - 1) - \frac{1}{2}(x - 1)^2 + \frac{1}{3}(x - 1)^3 - \frac{1}{4}(x - 1)^4 + \frac{1}{5}(x - 1)^5 + \cdots

Final Result

The Taylor series for f(x)=ln(x)f(x) = \ln(x) centered at c=1c = 1 is:

ln(x)=(x1)12(x1)2+13(x1)314(x1)4+15(x1)5+\ln(x) = (x - 1) - \frac{1}{2}(x - 1)^2 + \frac{1}{3}(x - 1)^3 - \frac{1}{4}(x - 1)^4 + \frac{1}{5}(x - 1)^5 + \cdots

Summary

  1. Taylor Series: The series converges for x>0x > 0.
  2. Radius of Convergence: The series converges in the interval (0,)(0, \infty).

Do you want details on any specific part of the calculation or have any questions? Here are some follow-up questions:

  1. What is the significance of the Taylor series in calculus?
  2. How would you derive the Taylor series for other functions, like exe^x?
  3. Can you explain the convergence criteria for Taylor series?
  4. What is the difference between a Taylor series and a Maclaurin series?
  5. How can you use the Taylor series for approximating values of ln(x)\ln(x)?

Tip: When working with Taylor series, always check the interval of convergence for accurate results.

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Math Problem Analysis

Mathematical Concepts

Calculus
Taylor Series
Differentiation

Formulas

f(x) = f(c) + f'(c)(x - c) + f''(c)/2!(x - c)^2 + f'''(c)/3!(x - c)^3 + ...

Theorems

Taylor's Theorem

Suitable Grade Level

Grades 11-12