What is the value of the coefficient of the 4th term in the expansion of (a + b)¹2?

Algebra and Trigonometry (6th Edition)
6th Edition
ISBN:9780134463216
Author:Robert F. Blitzer
Publisher:Robert F. Blitzer
ChapterP: Prerequisites: Fundamental Concepts Of Algebra
Section: Chapter Questions
Problem 1MCCP: In Exercises 1-25, simplify the given expression or perform the indicated operation (and simplify,...
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### Question 5: Binomial Expansion

**Question:**  
What is the value of the coefficient of the 4th term in the expansion of \((a + b)^{12}\)?

**Options:**  
- 985  
- 1,320  
- 220  
- 445  

**Explanation:**

To solve for the coefficient of the 4th term in the binomial expansion of \((a+b)^{12}\), we use the binomial theorem formula:

\[
(a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k
\]

For the 4th term, we need the term where \(k=3\) (note that binomial theorem terms are indexed starting from \(k=0\)). The binomial coefficient \(\binom{12}{3}\) determines the coefficient we're looking for. We can compute it as follows:

\[
\binom{12}{3} = \frac{12!}{3!(12-3)!} = \frac{12!}{3! \cdot 9!}
\]

This simplifies to:

\[
\frac{12 \times 11 \times 10}{3 \times 2 \times 1} = 220
\]

Therefore, the correct answer is:

- **220**

Feel free to use this derived explanation along with the question and provided options for educational purposes, helping students understand the binomial expansion and coefficient calculation methods.
Transcribed Image Text:### Question 5: Binomial Expansion **Question:** What is the value of the coefficient of the 4th term in the expansion of \((a + b)^{12}\)? **Options:** - 985 - 1,320 - 220 - 445 **Explanation:** To solve for the coefficient of the 4th term in the binomial expansion of \((a+b)^{12}\), we use the binomial theorem formula: \[ (a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k \] For the 4th term, we need the term where \(k=3\) (note that binomial theorem terms are indexed starting from \(k=0\)). The binomial coefficient \(\binom{12}{3}\) determines the coefficient we're looking for. We can compute it as follows: \[ \binom{12}{3} = \frac{12!}{3!(12-3)!} = \frac{12!}{3! \cdot 9!} \] This simplifies to: \[ \frac{12 \times 11 \times 10}{3 \times 2 \times 1} = 220 \] Therefore, the correct answer is: - **220** Feel free to use this derived explanation along with the question and provided options for educational purposes, helping students understand the binomial expansion and coefficient calculation methods.
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