Chapter 8: Problem 67
Find the sum for each series. $$\sum_{i=1}^{4}\left(3 i^{3}+2 i-4\right)$$
Short Answer
Expert verified
The sum is 304.
Step by step solution
01
Understand the Series Expression
The problem asks us to find the sum of the expression \(3i^3 + 2i - 4\) from \(i = 1\) to \(i = 4\). This means we need to substitute the values \(i = 1\), \(i = 2\), \(i = 3\), and \(i = 4\) into the expression, evaluate them, and then sum the results.
02
Substitute i = 1
Substitute \(i = 1\) into the expression: \(3(1)^3 + 2(1) - 4 = 3 + 2 - 4 = 1\).
03
Substitute i = 2
Substitute \(i = 2\) into the expression: \(3(2)^3 + 2(2) - 4 = 3(8) + 4 - 4 = 24 + 4 - 4 = 24\).
04
Substitute i = 3
Substitute \(i = 3\) into the expression: \(3(3)^3 + 2(3) - 4 = 3(27) + 6 - 4 = 81 + 6 - 4 = 83\).
05
Substitute i = 4
Substitute \(i = 4\) into the expression: \(3(4)^3 + 2(4) - 4 = 3(64) + 8 - 4 = 192 + 8 - 4 = 196\).
06
Sum the Results
Now add the results from each substitution: \(1 + 24 + 83 + 196 = 304\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Expression
A polynomial expression consists of variables raised to positive integer powers and their coefficients, combined using addition, subtraction, and multiplication. In our example, the expression \(3i^3 + 2i - 4\) is a polynomial with the variable \(i\). It has three terms:
- \(3i^3\): a cubic term, where \(3\) is the coefficient
- \(2i\): a linear term, with \(2\) as the coefficient
- \(-4\): a constant term, meaning it remains the same regardless of \(i\)
Sigma Notation
Sigma notation is a way to represent the sum of a series of terms that follow a pattern. It's succinct and powerful, especially for complex expressions with many terms. In the original problem, the sigma notation \(\sum_{i=1}^{4}\left(3i^3 + 2i - 4\right)\) tells us:
- \(\Sigma\) symbolizes the sum.
- \(i=1\) denotes the starting point for the variable \(i\).
- \(4\) is the ending point for \(i\).
- \(3i^3 + 2i - 4\) is the expression whose terms we sum by changing the variable \(i\) from 1 to 4.
Algebraic Substitution
Algebraic substitution is a straightforward process of replacing a variable in an expression with a number to evaluate the expression. For the series \(\sum_{i=1}^{4}(3i^3 + 2i - 4)\), substitution is the first critical step.
To substitute:
To substitute:
- Take the variable \(i\).
- Replace it with each integer value from 1 to 4 in the expression \(3i^3 + 2i - 4\).
- Calculate each individual expression's value.
- Substitute \(i = 1\) results in \(3(1)^3 + 2(1) - 4 = 1\).
- Substitute \(i = 2\) gives \(3(2)^3 + 2(2) - 4 = 24\).
- Continue similarly for \(i = 3\) and \(i = 4\).