Problem 50 - Algebra 2

Question

Find the specified term of each binomial expansion. Second term of \((x+3)^{9}\)

Step-by-Step Solution

Answer

The second term of \((x+3)^9\) is \(27x^8\).

Step 1: Calculating the binomial coefficient

The binomial coefficient can be calculated using the formula: \(\binom{n}{k} = \frac{n!}{k!(n-k)!}\). For this problem, you have \(n = 9\) and \(k = 1\), so you have \(\binom{9}{1} = \frac{9!}{1!(9-1)!} = 9\).

Step 2: Applying the Binomial Theorem

Now you can generate the second term by substituting \(a = x\), \(b = 3\), \(n = 9\), and \(k = 1\) into the Binomial theorem: \( \binom{n}{k} a^{(n-k)}b^k = 9 \cdot x^{9-1} \cdot 3^1 = 9 \cdot x^8 \cdot 3\). Computing \(9 \cdot 3 = 27\), therefore the second term is \(27x^8\).

Step 3: Final answer

The second term of the expansion of \((x+3)^9\) is \(27x^8\).

Key Concepts

Binomial Theorem

The binomial theorem is a fundamental principle in algebra used to expand expressions that are raised to a power. It provides a way of expressing any power of a binomial as a sum of terms. These terms incorporate coefficients, variables, and exponents.
In essence, for a binomial expression of the form \((a+b)^n\), the theorem states:\[(a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k\]This equation breaks down to show that each term in the expansion involves:

• A binomial coefficient \(\binom{n}{k}\)
• Power of the first term \(a\), denoted as \(a^{n-k}\)
• Power of the second term \(b\), denoted as \(b^k\)

Using this theorem simplifies finding specific terms without manually multiplying.For example, to find a specific term in the expansion of \((x+3)^9\), such as the second term, the binomial theorem allows us to use formulas rather than expanding the entire expression.

Binomial Coefficient

The binomial coefficient is a crucial part of the binomial theorem. It determines the weight of each term in a binomial expansion.The formula to calculate a binomial coefficient is:\[\binom{n}{k} = \frac{n!}{k!(n-k)!}\]

• \(n!\) ("n factorial") represents the product of all positive integers up to \(n\).
• \(k\) specifies which term you are dealing with in the expansion.

In our example, with the expression \((x+3)^9\), to find the second term, the values are \(n = 9\) and \(k = 1\).
This results in \(\binom{9}{1} = 9\).
Calculating binomial coefficients is foundational to understanding how the coefficients in the expanded form of a binomial expression are determined.

Exponents

Exponents are a compact notation used to denote repeated multiplication. In the context of binomial expansion, they help specify the degree of each term.
For a binomial expression \((a+b)^n\), exponents dictate:

• The power to which each component is raised.
• The distribution of powers between \(a\) and \(b\) across terms.

In each binomial expansion term, exponents are distributed as per binomial theorem rules:- The \(a\) term is raised to \(n-k\), which gradually decreases.- The \(b\) term is raised to \(k\), which gradually increases.
Considering our example \((x+3)^9\), in the second term, we have \(x^{9-1} = x^8\) and \(3^1\).
Through exponents, we balance the combination of both parts of the binomial, making exponents essential in crafting each term of the expansion.