Math Problem Statement

Find the Maclaurin series for the function

f(x)=ln(2+x).

Question 2

Select one:

a.

ln2−

n=1

x

n

n

2

n

b.

ln2−

n=1

x

n

n

c.

ln2−

n=1

(−1

)

n

x

n/

n

d.

ln2−

n=1

(−1

)

n

x

n/

n

2

n

Solution

To find the Maclaurin series for the function f(x)=ln(2+x)f(x) = \ln(2 + x), we need to express this function as a power series around x=0x = 0.

Step-by-step Solution:

  1. Recall the Maclaurin series formula for ln(1+u)\ln(1 + u):

    The Maclaurin series for ln(1+u)\ln(1 + u) is: ln(1+u)=n=1(1)n+1nun,for u<1.\ln(1 + u) = \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n} u^n, \quad \text{for } |u| < 1.

    We want to rewrite ln(2+x)\ln(2 + x) in a form that makes it easier to use this formula.

  2. Rewrite ln(2+x)\ln(2 + x):

    Set u=x2u = \frac{x}{2}, then we have: ln(2+x)=ln(2(1+x2)).\ln(2 + x) = \ln \left(2 \left(1 + \frac{x}{2}\right) \right). Using the logarithmic property ln(ab)=lna+lnb\ln(ab) = \ln a + \ln b, this becomes: ln(2+x)=ln2+ln(1+x2).\ln(2 + x) = \ln 2 + \ln \left(1 + \frac{x}{2}\right).

    Now, we can apply the Maclaurin series expansion for ln(1+u)\ln(1 + u) with u=x2u = \frac{x}{2}:

    ln(1+x2)=n=1(1)n+1n(x2)n.\ln(1 + \frac{x}{2}) = \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n} \left(\frac{x}{2}\right)^n.

  3. Simplify the series:

    Substitute this series back into the expression for ln(2+x)\ln(2 + x):

    ln(2+x)=ln2+n=1(1)n+1n(x2)n.\ln(2 + x) = \ln 2 + \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n} \left(\frac{x}{2}\right)^n.

    This can be written as:

    ln(2+x)=ln2+n=1(1)n+1nxn2n.\ln(2 + x) = \ln 2 + \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n} \frac{x^n}{2^n}.

  4. Rewrite the series to match the provided options:

    We have:

    ln(2+x)=ln2n=1(1)nnxn2n.\ln(2 + x) = \ln 2 - \sum_{n=1}^{\infty} \frac{(-1)^n}{n} \frac{x^n}{2^n}.

    This is equivalent to:

    ln(2+x)=ln2n=1(1)nxnn2n.\ln(2 + x) = \ln 2 - \sum_{n=1}^{\infty} \frac{(-1)^n x^n}{n \cdot 2^n}.

Conclusion:

This matches with Option D:

D. ln2n=1(1)nxnn2n.\textbf{D. } \ln 2 - \sum_{n=1}^{\infty} \frac{(-1)^n x^n}{n \cdot 2^n}.

Final Answer:

The correct answer is (d).

Would you like further details or explanations? Here are 5 related questions you might find interesting:

  1. How do you derive the Maclaurin series for other logarithmic functions like ln(1+x)\ln(1 + x)?
  2. What is the radius of convergence for the series representation of ln(2+x)\ln(2 + x)?
  3. How does the series expansion change for higher derivatives of ln(2+x)\ln(2 + x)?
  4. Can you use the Maclaurin series to approximate ln(2.1)\ln(2.1)?
  5. What are the applications of logarithmic series in solving integrals?

Tip: For series convergence, always check the interval of convergence, especially when substituting variables or using logarithmic expansions.

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Math Problem Analysis

Mathematical Concepts

Maclaurin series
Logarithmic functions

Formulas

Maclaurin series for ln(1 + u)

Theorems

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Suitable Grade Level

College