Chapter 8: Problem 44
Write the sum of each geometric series as a rational number. $$0.36+0.0036+0.000036+\cdots$$
Short Answer
Expert verified
The sum of the series is \( \frac{4}{11} \).
Step by step solution
01
Identify the First Term
The first term of the series is given as \( a = 0.36 \). This is the starting point for our geometric series.
02
Determine the Common Ratio
To find the common ratio \( r \), divide the second term by the first term: \( r = \frac{0.0036}{0.36} = 0.01 \).
03
Use the Formula for the Sum of an Infinite Geometric Series
The formula for the sum \( S \) of an infinite geometric series when \(|r| < 1\) is \( S = \frac{a}{1 - r} \).
04
Calculate the Sum
Plug the values of \( a = 0.36 \) and \( r = 0.01 \) into the formula: \( S = \frac{0.36}{1 - 0.01} = \frac{0.36}{0.99} \).
05
Simplify the Fraction
Convert the decimal \( \frac{0.36}{0.99} \) to a simple fraction by multiplying the numerator and denominator by 100: \( \frac{36}{99} = \frac{4}{11} \) after simplification.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Infinite Series
An infinite series is a sum of an infinite sequence of terms. Unlike a finite series, which has a definite number of terms and a sum that we can easily find, an infinite series continues indefinitely. The key challenge with infinite series is determining whether they have a sum. Not all infinite series sum to a finite number, but for those that do, there are specific conditions.
- A series converges if it approaches a specific value as more terms are added.
- If a series does not approach a specific value, it diverges.
Sum of Series
Finding the sum of a series can be simple or complex, depending on the series type. For a geometric series, there's a handy formula that applies only when the series converges. This is the case when the common ratio's absolute value is less than 1.The formula is:\[S = \frac{a}{1 - r}\]where:
- \( a \) is the first term, and
- \( r \) is the common ratio of the series.
Common Ratio
The common ratio is crucial in determining the behavior of a geometric series. In essence, it tells us how each term in the series relates to the previous one. A constant factor that you multiply by each time to get to the next term.
- If the common ratio is positive or negative but less than 1 in absolute terms, the series will converge.
- If the ratio is greater than 1 or less than -1, the series will diverge.