Math Problem Statement

Find the Maclaurin’s series for the function 𝑓(𝑥) given by 𝑓(𝑥) = 1/(1−𝑥)

Solution

To find the Maclaurin series for the function f(x)=11xf(x) = \frac{1}{1-x}, we start by recalling the general definition of a Maclaurin series:

f(x)=f(0)+f(0)x+f(0)x22!+f(3)(0)x33!+f(x) = f(0) + f'(0)x + \frac{f''(0)x^2}{2!} + \frac{f^{(3)}(0)x^3}{3!} + \dots

Step-by-step Solution:

  1. Start with the function: f(x)=11x.f(x) = \frac{1}{1-x}.

  2. Find the derivatives of f(x)f(x):

    • First derivative: f(x)=ddx(11x)=1(1x)2.f'(x) = \frac{d}{dx}\left(\frac{1}{1-x}\right) = \frac{1}{(1-x)^2}.
    • Second derivative: f(x)=ddx(1(1x)2)=2(1x)3.f''(x) = \frac{d}{dx}\left(\frac{1}{(1-x)^2}\right) = \frac{2}{(1-x)^3}.
    • Third derivative: f(3)(x)=ddx(2(1x)3)=6(1x)4.f^{(3)}(x) = \frac{d}{dx}\left(\frac{2}{(1-x)^3}\right) = \frac{6}{(1-x)^4}.
    • For the nn-th derivative: f(n)(x)=n!(1x)n+1.f^{(n)}(x) = \frac{n!}{(1-x)^{n+1}}.
  3. Evaluate each derivative at x=0x = 0:

    • f(0)=1f(0) = 1,
    • f(0)=1f'(0) = 1,
    • f(0)=2f''(0) = 2,
    • f(3)(0)=6f^{(3)}(0) = 6,
    • f(n)(0)=n!f^{(n)}(0) = n!.
  4. Substitute these values into the Maclaurin series formula: f(x)=f(0)+f(0)x+f(0)x22!+f(3)(0)x33!+f(x) = f(0) + f'(0)x + \frac{f''(0)x^2}{2!} + \frac{f^{(3)}(0)x^3}{3!} + \dots f(x)=1+x+2x22!+6x33!+f(x) = 1 + x + \frac{2x^2}{2!} + \frac{6x^3}{3!} + \dots

  5. Simplify the series: Each term simplifies as: n!xnn!=xn.\frac{n!x^n}{n!} = x^n. Thus: f(x)=1+x+x2+x3+f(x) = 1 + x + x^2 + x^3 + \dots

  6. Write the Maclaurin series in summation form: f(x)=n=0xn,for x<1.f(x) = \sum_{n=0}^\infty x^n, \quad \text{for } |x| < 1.

Final Result:

The Maclaurin series for f(x)=11xf(x) = \frac{1}{1-x} is: f(x)=n=0xn,x<1.f(x) = \sum_{n=0}^\infty x^n, \quad |x| < 1.

Would you like further details or a graphical representation?
Here are 5 related questions and a tip for deeper understanding:

  1. How does the radius of convergence x<1|x| < 1 arise in this series?
  2. What happens if xx is outside the interval of convergence?
  3. Can you derive the Maclaurin series for 1(1x)2\frac{1}{(1-x)^2} using a similar method?
  4. How does the Maclaurin series for ln(1+x)\ln(1+x) compare to this one?
  5. How would the series change if f(x)=11+xf(x) = \frac{1}{1+x}?

Tip: The geometric series sum n=0xn=11x\sum_{n=0}^\infty x^n = \frac{1}{1-x} is foundational in calculus—master it, and many series expansions become easier!

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Math Problem Analysis

Mathematical Concepts

Series Expansion
Maclaurin Series
Geometric Series
Calculus

Formulas

Maclaurin Series Formula: f(x) = f(0) + f'(0)x + f''(0)x^2/2! + f'''(0)x^3/3! + ...
Maclaurin Series for 1/(1-x): f(x) = ∑_{n=0}^{∞} x^n

Theorems

Maclaurin Series Theorem
Geometric Series Theorem

Suitable Grade Level

Grades 11-12