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Example: Finding the Sum of a Geometric Series Given in Summation Notation
Find the sum .
Because the series is expressed in sigma notation, start by identifying the values needed for the sum formula : the first term , the common ratio , and the number of terms . Write out the first few terms by substituting successive values of :
which gives
Identify : the first term is .
Find the common ratio by dividing consecutive terms: and , so .
The upper limit of the summation gives . Substitute , , and into the formula:
Simplify:
This example illustrates how to evaluate a geometric series that is presented in summation notation: expand the first few terms to determine and , read from the upper limit, and then apply the partial-sum formula.
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Ch.12 Sequences, Series and Binomial Theorem - Intermediate Algebra @ OpenStax
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Example: Finding the Sum of a Geometric Series Given in Summation Notation
A utility company is modeling the total renewable energy output of a wind farm over its first 12 years of operation. The total output (in megawatt-hours) is represented by the geometric series: . Based on the standard form of a geometric series , what is the value of the common ratio in this expression?
A social media manager uses the expression to project the total number of new followers gained over a 6-month period. Match each component of this summation notation to its specific role in the geometric series.
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Identifying Components of a Geometric Summation
A sales manager is auditing a projected revenue model represented by the geometric summation . To verify the monthly growth rate (common ratio), the manager decides to calculate the first two terms of the series and find their ratio. Arrange the following steps in the correct order to find using this method.
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As a business analyst projecting cumulative sales revenue, you are working with a growth model expressed in summation notation as . To calculate the total projected revenue using the geometric sum formula , you must first determine the values of the variables. Based on the process for evaluating a geometric series in this notation, how do you correctly identify the value of the first term, ?
A project manager is calculating the cumulative cost of a logistics expansion project where costs grow geometrically over 15 months, modeled by the summation . To find the total cost using the partial-sum formula , the manager must extract the correct variables from the notation. Arrange the following steps in the correct order to identify these variables and prepare for the final calculation.
A corporate inventory manager is modeling the total stock requirements for a 15-day peak period using the geometric series . To calculate the total using the partial-sum formula , match each variable from the formula with its correct value or role as identified in the summation notation.
A corporate logistics coordinator is modeling the total distance traveled by a delivery fleet over a 24-day period using the geometric series . To calculate the total sum using the partial-sum formula , the coordinator must first identify the number of terms to be summed (). Based on the summation notation provided, the value of is ____.
A corporate production manager uses the summation to model the total units manufactured over 15 shifts. True or False: When applying the partial-sum formula to calculate the total output, the value for the first term is equal to 2.