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Without expanding completely, find the indicated term(s) in the expansion of the expression. \(\left(3 y^{3}-2 x^{2}\right)^{4} ; \quad\) term that contains \(y^{9}\)

Short Answer

Expert verified
The required term is \(-216x^2y^9\).

Step by step solution

01

Understand the Binomial Theorem

The expression \((a + b)^n\) can be expanded using the Binomial Theorem, which states it as \( \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k \). Here, we have \(a = 3y^3\) and \(b = -2x^2\) with \(n = 4\). We are tasked to identify a term in the expansion that involves \(y^9\).
02

Set the Exponential Powers for \(y\)

In the binomial expansion, each term takes the form \( \binom{4}{k} (3y^3)^{4-k} (-2x^2)^k \). We need to find the value of \(k\) for which \(y^{3(4-k)} = y^9\).
03

Solve for k

Set the exponent of \(y\) to 9: \(3(4-k) = 9\). Solving for \(k\), we get:\[ 3(4-k) = 9 \]\[ 12 - 3k = 9 \]\[ 3k = 3 \]\[ k = 1 \].
04

Find the Coefficient of the Target Term

Substitute \(k = 1\) into the term from the binomial expansion.\[ \binom{4}{1} (3y^3)^{4-1} (-2x^2)^1 \]Calculate each component:- \(\binom{4}{1} = 4\)- \((3y^3)^3 = 27y^9\)- \((-2x^2)^1 = -2x^2\).Thus, the term is:\[ 4 \times 27y^9 \times (-2x^2) = -216x^2y^9 \].
05

Identify the Required Term

The term containing \(y^9\) in the expansion is \(-216x^2y^9\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Binomial Expansion
The Binomial Theorem is a powerful algebraic tool that allows us to expand expressions of the form \((a + b)^n\) into a sum of terms. The theorem states:\[(a + b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k\]- \(n\) represents the exponent applied to the binomial.- \(\binom{n}{k}\) denotes the binomial coefficient, calculated as \(\frac{n!}{k!(n-k)!}\).- Each term in the expansion has a specific structure: \(a^{n-k}\) and \(b^k\) are combined to form the terms.The term \(\binom{n}{k} a^{n-k} b^k\) is derived by selecting the appropriate combinations of the terms \(a\) and \(b\). In exercises like the given problem, the goal is often to find specific terms without performing a full expansion. This method streamlines solving complex binomial expressions.
Polynomial Terms
Polynomial terms are components of a larger polynomial expression, which are usually combined using addition or subtraction. In our problem, each term of the binomial expansion \((3y^3 - 2x^2)^4\) will be a polynomial term. Key aspects include:
  • Each term is defined by powers: Terms have distinct powers of variables, like \(y^9\) in this problem, which helps target specific terms during expansions.
  • Coefficients play a critical role: Coefficients are numeric factors that multiply the variables, derived from binomial coefficients and constant terms.
In practical problems, identifying the term structure is crucial. For instance, understanding that our target term must include \(y^9\) helps us narrow down the specific combination of powers and coefficients that form the desired term.
Exponent Rules
Exponent rules are the foundation for manipulating expressions with powers. They enable us to handle terms like \(y^9\) efficiently. Here are some fundamental rules:
  • Power of a power: \((a^m)^n = a^{mn}\) ensures that when powers are nested, they multiply, like \((y^3)^3 = y^9\).
  • Multiplying powers with the same base: \(a^m \times a^n = a^{m+n}\) is essential for combining like terms within an expression.
In exercises involving polynomial expansions, applying these rules correctly allows us to quickly identify and manage terms like \(y^9\). It simplifies finding the power or degree of the polynomial that matches the desired term condition.

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