Chapter 5: Problem 102
Perform the indicated operations. $$ (3 a-2 b)^{3} $$
Short Answer
Expert verified
The expanded expression is \(27a^3 - 54a^2b + 36ab^2 - 8b^3\).
Step by step solution
01
Expand the Expression
To expand \((3a - 2b)^3\), we will apply the binomial theorem. According to the binomial theorem, \((x + y)^n = \sum_{k=0}^{n} \binom{n}{k} x^{n-k} y^{k}\). In this case, \(x = 3a\), \(y = -2b\), and \(n = 3\).
02
Apply Binomial Coefficients
The binomial coefficients for cubic terms are \(\binom{3}{0}\), \(\binom{3}{1}\), \(\binom{3}{2}\), and \(\binom{3}{3}\). These coefficients are 1, 3, 3, and 1, respectively. We will use these to expand the expression.
03
Substitute and Simplify Terms
Using the binomial coefficients, expand the terms:\[ (3a - 2b)^3 = \binom{3}{0}(3a)^3(-2b)^0 + \binom{3}{1}(3a)^2(-2b)^1 + \binom{3}{2}(3a)^1(-2b)^2 + \binom{3}{3}(3a)^0(-2b)^3 \]Calculating each term:\(= 1 imes (27a^3) imes 1 + 3 imes (9a^2) imes (-2b) + 3 imes (3a) imes (4b^2) + 1 imes 1 imes (-8b^3)\).
04
Calculate the Expression
Replace and simplify:\[ (3a - 2b)^3 = 27a^3 - 54a^2b + 36ab^2 - 8b^3 \].
05
Final Simplified Expression
Combine all the terms from the expanded expression to get the final result:\[ 27a^3 - 54a^2b + 36ab^2 - 8b^3 \] is the fully expanded result of \((3a - 2b)^3\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Expansion
Polynomial expansion is a process of expressing a power of a binomial as a sum of terms involving powers of its components. Essentially, it's about decomposing a given expression, like \((3a - 2b)^3\), into its expanded form.Using formulas provided by the binomial theorem, we can expand polynomials systematically. This theorem states that \((x + y)^n\) can be expanded into a series:
- Each term in this series has the form \(\binom{n}{k} x^{n-k} y^k\), where \(k\) varies from \(0\) to \(n\).
- In our example, \((3a - 2b)^3\), the task is to determine each term in the expansion using the components \(3a\) and \(-2b\), with an exponent of 3.
Cubic Expressions
Cubic expressions involve raising a binomial to the third power, which results in a polynomial of degree three. In this specific case of \((3a - 2b)^3\), our goal is to find the expanded polynomial.Cubic expressions always result in 4 terms. Here's why:
- For a term like \((3a - 2b)^3\), the highest degree term is \(a^3\), which means this term will have three factors of \(a\).
- The next terms decrease in the power of \(a\) while increasing in the power of \(b\), until reaching \(b^3\).
Binomial Coefficients
The binomial coefficients are key to expanding expressions such as \((3a - 2b)^3\). These coefficients determine the weight of each term in the expansion and are derived from Pascal's triangle.When expanding a cubic expression, the binomial coefficients are found using combinations \(\binom{n}{k}\):
- \(\binom{3}{0} = 1\) is the coefficient for the first term.
- \(\binom{3}{1} = 3\) applies to the second term.
- \(\binom{3}{2} = 3\) is for the third term.
- \(\binom{3}{3} = 1\) for the final term.