Math Problem Statement

Find the sum of the series: 1 / (4e^2) - 1 / (8e^3) + 1 / (16e^4) - 1 / (32e^5) + ...

Solution

The given series is:

14e218e3+116e4132e5+\frac{1}{4e^2} - \frac{1}{8e^3} + \frac{1}{16e^4} - \frac{1}{32e^5} + \dots

We can identify that this is an infinite geometric series where the terms alternate in sign.


Step 1: General term of the series

The series can be written as: S=aar+ar2ar3+S = a - ar + ar^2 - ar^3 + \dots

Here:

  • a=14e2a = \frac{1}{4e^2} (first term),
  • r=12er = -\frac{1}{2e} (common ratio).

Step 2: Sum of an infinite geometric series

The sum SS of an infinite geometric series is given by:

S=a1rwhere r<1.S = \frac{a}{1 - r} \quad \text{where } |r| < 1.


Step 3: Substitute values

We substitute a=14e2a = \frac{1}{4e^2} and r=12er = -\frac{1}{2e} into the formula:

S=14e21(12e).S = \frac{\frac{1}{4e^2}}{1 - \left(-\frac{1}{2e}\right)}.

Simplify the denominator:

1(12e)=1+12e.1 - \left(-\frac{1}{2e}\right) = 1 + \frac{1}{2e}.

Thus:

S=14e21+12e.S = \frac{\frac{1}{4e^2}}{1 + \frac{1}{2e}}.


Step 4: Simplify further

To simplify 1+12e1 + \frac{1}{2e}, we find a common denominator:

1+12e=2e+12e.1 + \frac{1}{2e} = \frac{2e + 1}{2e}.

Now rewrite SS:

S=14e22e+12e.S = \frac{\frac{1}{4e^2}}{\frac{2e + 1}{2e}}.

Dividing by a fraction is equivalent to multiplying by its reciprocal:

S=14e22e2e+1.S = \frac{1}{4e^2} \cdot \frac{2e}{2e + 1}.

Simplify:

S=2e4e2(2e+1).S = \frac{2e}{4e^2 (2e + 1)}.

Simplify the numerator and denominator:

S=12e(2e+1).S = \frac{1}{2e (2e + 1)}.


Final Answer:

The sum of the series is:

12e(2e+1).\boxed{\frac{1}{2e (2e + 1)}}.

Let me know if you would like me to explain any step in more detail!


Related Questions:

  1. What is the formula for the sum of an infinite geometric series?
  2. How do you find the common ratio of a series?
  3. What is the condition for convergence of an infinite geometric series?
  4. Can you solve a similar series where the ratio is not alternating?
  5. What happens if the common ratio rr is greater than or equal to 11?

Tip: Always check whether the common ratio r<1|r| < 1 before applying the infinite geometric series formula.

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Math Problem Analysis

Mathematical Concepts

Infinite Geometric Series
Algebra
Convergence of Series

Formulas

Sum of an infinite geometric series: S = a / (1 - r) where |r| < 1
Simplification of algebraic fractions

Theorems

Infinite Geometric Series Sum Theorem

Suitable Grade Level

Grades 10-12