Chapter 10: Problem 38
Find the coefficient \(C\) of the given term in each binomial expansion. Binomial Term $$(3+y)^{9} \quad c y^{5}$$
Short Answer
Expert verified
The coefficient \(C\) for the term \(y^5\) in \((3+y)^9\) is 10206.
Step by step solution
01
Identify the Binomial Expansion Formula
The binomial expansion of \((a+b)^n\) is given by \(\sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k\). We need to use this formula to expand \((3+y)^9\).
02
Match the Term to the Formula
We need to find the coefficient of the term which includes \(y^5\) in the expansion of \((3+y)^9\). In the formula, \(b = y\) and the power \(k = 5\).
03
Calculate the Binomial Coefficient
The binomial coefficient can be calculated as \(\binom{9}{5}\). This represents the number of ways to choose 5 elements from a set of 9, and is calculated as \(\frac{9!}{5!(9-5)!}\).
04
Simplify the Binomial Coefficient
Calculate \(\binom{9}{5} = \frac{9 \times 8 \times 7 \times 6}{4 \times 3 \times 2 \times 1} = 126\).
05
Determine the Coefficient from the Expanded Term
In the term \(\binom{9}{5} a^{9-5} b^5\), substitute \(a = 3\), \(b = y\). This gives us \(126 \times 3^{4} \times y^5\).
06
Calculate the Final Coefficient
Calculate \(3^4 = 81\). The coefficient \(C\) is thus \(126 \times 81 = 10206\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Binomial Coefficient
The binomial coefficient is a crucial concept in the world of algebra, especially when dealing with expressions that require expansion. It essentially counts how many ways you can choose \( k \) items from a larger set of \( n \) items, represented as \[ \binom{n}{k} \]. This concept is mathematically expressed as \[ \binom{n}{k} = \frac{n!}{k!(n-k)!} \], where \( ! \) denotes a factorial, which is the product of all positive integers up to a certain number.
- For example, finding \( \binom{9}{5} \) means calculating the ways to choose 5 items from a total of 9, and is computed as \[ \frac{9 \times 8 \times 7 \times 6}{4 \times 3 \times 2 \times 1} = 126 \].
- This coefficient is not merely a mathematical curiosity; it is the weight or multiplier for each term in the expansion of a binomial expression.
Binomial Theorem
The Binomial Theorem is a powerful algebraic tool that describes how to expand expressions that are raised to a power, such as \( (a+b)^n \). This theorem provides a straightforward way to expand polynomials without manually multiplying the binomials.According to the Binomial Theorem, any binomial expression \( (a+b)^n \) can be expanded using the formula \[ \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k \].
- Each term in this expansion is multiplied by a binomial coefficient \( \binom{n}{k} \), which we learned counts the number of ways to choose items in combinations, making it central to finding term coefficients in binomial expansions.
- This formula efficiently helps list out each term in the expansion, calculated for specified powers in descending order of \( a \) and ascending order of \( b \).
Polynomial Expansion
When expanding polynomials using the Binomial Theorem, you are potentially simplifying a complex expression into a series of terms. Each term results from specifying values of \( a \), \( b \), and \( n \) from our binomial expression.In a typical polynomial expansion of \( (3+y)^9 \), for instance, we use the theorem to break down and redefine its terms based on powers of \( y \) and constants multiplied by coefficients.
- The term connected to \( y^5 \) involves determining its coefficient through \( \binom{9}{5} \), substituting the value of \( a \) (in our example, 3), raising it to the appropriate power, and then multiplying by \( b^5 \).
- Using these steps, we find specific terms like 126 for the coefficient, resulting in the expression \( 126 \times 3^4 \times y^5 \), and at the end, evaluating 3 to the power of 4 results in 81, which ultimately gives us a total coefficient of 10,206 when calculated thoroughly.