Chapter 14: Problem 14
Evaluate. See Example 1 $$ \sum_{i=2}^{4} i(i-3) $$
Short Answer
Expert verified
The summation evaluates to 2.
Step by step solution
01
Understand the Summation
The problem involves evaluating the summation \( \sum_{i=2}^{4} i(i-3) \). This means we need to substitute each integer from 2 to 4 into the expression \( i(i-3) \) and add the results.
02
Substitute and Evaluate for Each Term
First, substitute \(i = 2\) into the expression: \[ 2 (2-3) = 2 \times (-1) = -2 \]Next, substitute \(i = 3\): \[ 3 (3-3) = 3 \times 0 = 0 \]Finally, substitute \(i = 4\): \[ 4 (4-3) = 4 \times 1 = 4 \]
03
Sum All Terms
Add the results of each evaluated term: \[ -2 + 0 + 4 = 2 \]
04
Write the Final Answer
The summation yields a final result of 2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Evaluating Summations
In algebra, evaluating summations involves finding the sum of a sequence of numbers governed by a specific rule or expression. This process can often be seen as a simplification of a series of repeated arithmetic operations. For example, the summation notation \( \sum_{i=2}^{4} i(i-3) \) prompts us to apply the expression \( i(i-3) \) to each integer from 2 to 4, and then sum those results.
Follow these steps:
Follow these steps:
- Identify the range of values for which the expression will be calculated. In this exercise, the values are \( i = 2, 3, 4 \).
- Substitute each integer into the expression to calculate individual terms. For instance, substituting \(i=2\) yields \(2 \times (2-3) = -2\).
- Sum all evaluated terms together. Using our example, adding \(-2, 0,\) and \(4\) results in \(2\).
Algebraic Expressions
Algebraic expressions are combinations of numbers, variables, and operations that represent a particular quantity. In the context of summations, an algebraic expression often defines the rule by which individual terms in the summation are calculated.
In our exercise, \(i(i-3)\) is the algebraic expression to be evaluated for each integer value in the range specified by the summation. Breaking it down:
In our exercise, \(i(i-3)\) is the algebraic expression to be evaluated for each integer value in the range specified by the summation. Breaking it down:
- \(i\) is a variable that changes according to the specified range—here, 2 through 4.
- \((i-3)\) involves a simple operation that shifts each \(i\) value by subtracting 3, giving a new integer to multiply by \(i\).
- Multiplication of \(i\) and \((i-3)\) generates terms like \(-2, 0, \) and \(4\).
Summation Notation
Summation notation, often expressed with the Greek letter Sigma (\(\sum\)), provides a powerful shorthand for representing the sum of a sequence governed by an algebraic expression. It avoids lengthy addition of terms by using concise expressions.
Consider the segment \(\sum_{i=2}^{4} i(i-3)\):
Consider the segment \(\sum_{i=2}^{4} i(i-3)\):
- The symbol \(\sum\) signifies that a sum will be calculated.
- The subscript \(i=2\) indicates the starting value for \(i\).
- The number 4 at the upper limit shows the ending value for \(i\).
- The expression \(i(i-3)\) within the summation tells us what calculation to perform for each \(i\) from 2 to 4.