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Ch. 8 - Sequences, Induction, and Probability
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook
All textbooksBlitzer 8th EditionCh. 8 - Sequences, Induction, and ProbabilityProblem 35
Chapter 9, Problem 35

Find each indicated sum. ∑i=14(−12)i\(\sum\)_{i=1}^{4} \(\left\)(-\(\frac{1}{2}\]\right\))^{i}

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Identify the sum notation: you need to find the sum of the terms from \( i = 1 \) to \( i = 4 \) of the expression \( \left(-\frac{1}{2}\right)^i \). This means you will add \( \left(-\frac{1}{2}\right)^1 + \left(-\frac{1}{2}\right)^2 + \left(-\frac{1}{2}\right)^3 + \left(-\frac{1}{2}\right)^4 \).
Recognize that this is a geometric series where the first term \( a = \left(-\frac{1}{2}\right)^1 = -\frac{1}{2} \) and the common ratio \( r = -\frac{1}{2} \).
Recall the formula for the sum of the first \( n \) terms of a geometric series: \[ S_n = a \cdot \frac{1 - r^n}{1 - r} \]. Here, \( n = 4 \).
Substitute the values into the formula: \[ S_4 = \left(-\frac{1}{2}\right) \cdot \frac{1 - \left(-\frac{1}{2}\right)^4}{1 - \left(-\frac{1}{2}\right)} \].
Simplify the numerator and denominator separately, then multiply by the first term to find the sum. Remember not to calculate the final numeric value, just set up the expression.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Summation Notation (Sigma Notation)

Summation notation uses the Greek letter sigma (Σ) to represent the sum of a sequence of terms. It specifies the index of summation, the starting and ending values, and the general term to be added. Understanding this notation is essential to correctly interpret and compute the sum.
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Interval Notation

Geometric Series

A geometric series is a sum of terms where each term is found by multiplying the previous term by a constant ratio. Recognizing the series as geometric allows the use of formulas to find the sum efficiently, especially when the number of terms is finite.
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Formula for the Sum of a Finite Geometric Series

The sum of the first n terms of a geometric series with initial term a and common ratio r (r ≠ 1) is given by S_n = a(1 - r^n) / (1 - r). This formula simplifies the calculation of sums without adding each term individually.
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