Math Problem Statement

series from n = 0 to infinity of (8+2^n)/5^n

Solution

The series in question is:

n=08+2n5n\sum_{n=0}^{\infty} \frac{8 + 2^n}{5^n}

We can break it down into two separate sums:

n=085n+n=02n5n\sum_{n=0}^{\infty} \frac{8}{5^n} + \sum_{n=0}^{\infty} \frac{2^n}{5^n}

Step 1: Evaluate the first sum:

n=085n\sum_{n=0}^{\infty} \frac{8}{5^n}

This is a geometric series with the first term a=8a = 8 and the common ratio r=15r = \frac{1}{5}. The sum of an infinite geometric series is given by:

S=a1rS = \frac{a}{1 - r}

Substituting the values:

S1=8115=845=8×54=10S_1 = \frac{8}{1 - \frac{1}{5}} = \frac{8}{\frac{4}{5}} = 8 \times \frac{5}{4} = 10

Step 2: Evaluate the second sum:

n=02n5n\sum_{n=0}^{\infty} \frac{2^n}{5^n}

This is also a geometric series with the first term a=1a = 1 (since 2050=1\frac{2^0}{5^0} = 1) and the common ratio r=25r = \frac{2}{5}. Using the formula for the sum of an infinite geometric series:

S2=1125=135=53S_2 = \frac{1}{1 - \frac{2}{5}} = \frac{1}{\frac{3}{5}} = \frac{5}{3}

Step 3: Combine the results:

Now, we sum both parts:

S=S1+S2=10+53S = S_1 + S_2 = 10 + \frac{5}{3}

To simplify:

S=10+53=303+53=353S = 10 + \frac{5}{3} = \frac{30}{3} + \frac{5}{3} = \frac{35}{3}

Thus, the value of the series is:

353\boxed{\frac{35}{3}}

Would you like more details on any part of the process, or do you have any follow-up questions? Here are some related questions you might find interesting:

  1. How does the sum formula for a geometric series apply in different contexts?
  2. Can we derive similar sums for series with different exponents or more complex terms?
  3. What happens if the common ratio rr is greater than 1?
  4. How do we test the convergence of a series before summing it?
  5. How can we generalize this method to handle series with multiple variables or more complex expressions?

Tip: Always check the common ratio rr when dealing with geometric series. If r1|r| \geq 1, the series will not converge.

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Math Problem Analysis

Mathematical Concepts

Series
Geometric Series
Infinite Series
Summation

Formulas

Sum of infinite geometric series: S = a / (1 - r)

Theorems

Geometric Series Convergence
Sum of Geometric Series

Suitable Grade Level

Grades 10-12