Chapter 5: Problem 5
Find the value of the indicated sum. $$ \sum_{m=1}^{8}(-1)^{m} 2^{m-2} $$
Short Answer
Expert verified
The sum is \( \frac{85}{2} \).
Step by step solution
01
Understand the Summation Notation
The problem requires us to compute \( \sum_{m=1}^{8}(-1)^{m} 2^{m-2} \). This means that we need to calculate the sum by substituting integer values from 1 to 8 into the expression \((-1)^{m} 2^{m-2}\) and adding all those expressions together.
02
Calculate Each Term of the Series
Substitute each integer from 1 to 8 into the expression to obtain each term of the series.- For \( m = 1 \), the term is \((-1)^{1} 2^{1-2} = -\frac{1}{2}\).- For \( m = 2 \), the term is \((-1)^{2} 2^{2-2} = 1\).- For \( m = 3 \), the term is \((-1)^{3} 2^{3-2} = -2\).- For \( m = 4 \), the term is \((-1)^{4} 2^{4-2} = 4\).- For \( m = 5 \), the term is \((-1)^{5} 2^{5-2} = -8\).- For \( m = 6 \), the term is \((-1)^{6} 2^{6-2} = 16\).- For \( m = 7 \), the term is \((-1)^{7} 2^{7-2} = -32\).- For \( m = 8 \), the term is \((-1)^{8} 2^{8-2} = 64\).
03
Sum All Terms Together
Now, add all the calculated terms together: \[-\frac{1}{2} + 1 - 2 + 4 - 8 + 16 - 32 + 64\].First, simplify these terms in groups for easier calculation:1. \(-\frac{1}{2} + 1 = \frac{1}{2} \).2. \( \frac{1}{2} - 2 = -\frac{3}{2} \).3. \(-\frac{3}{2} + 4 = \frac{5}{2} \).4. \( \frac{5}{2} - 8 = -\frac{11}{2} \).5. \(-\frac{11}{2} + 16 = \frac{21}{2} \).6. \( \frac{21}{2} - 32 = -\frac{43}{2} \).7. \(-\frac{43}{2} + 64 = \frac{85}{2} \).
04
Present the Final Result
The calculated sum is \( \frac{85}{2} \), which completes the evaluation of the sum.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Series Calculation
Series calculation involves finding the sum of a sequence of numbers, often using summation notation. In this problem, we have a series defined by the expression \((-1)^{m} 2^{m-2}\), where \(m\) takes integer values from 1 to 8. Each term of the series is calculated by substituting these integer values into the expression.
- For \(m = 1\) to \(m = 8\), you compute each term individually, giving us a sequence of terms: \(-\frac{1}{2}, 1, -2, 4, -8, 16, -32,\) and \(64\).
- Summing these terms together involves adding both positive and negative values, requiring careful attention to signs and magnitudes.
Alternating Series
An alternating series is a series where the signs of its terms alternate between positive and negative. This is a defining feature of the series \( \sum_{m=1}^{8}(-1)^{m} 2^{m-2} \), where the \((-1)^{m}\) factor causes each term to switch signs.
- Observe how, for odd \(m\), the term \((-1)^{m}\) results in a negative value, while for even \(m\), it results in a positive value.
- This alternating pattern often impacts the convergence or the final summation of the series, as negative and positive terms successively cancel each other out partially.
Exponential Function
The expression \(2^{m-2}\) in our series is an example of an exponential function, where the base (2 in this case) is raised to a power determined by the variable \(m-2\). Exponential functions grow rapidly, especially in the context of powers rising from negative to positive.
- In our series, as \(m\) increases, \(2^{m-2}\) evolves from a fractional power at \(m=1\) to a substantial positive integer at \(m=8\).
- Exponential growth makes earlier terms with smaller exponents relatively smaller in magnitude compared to those with larger exponents.