Math Problem Statement

Use the binomial theorem to expand the binomial (4a - b)^3. Move the correct answer to each box.

Solution

To solve this question, we use the Binomial Theorem, which states:

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

Here, the given binomial is (4ab)3(4a - b)^3. We will expand this step-by-step.


Step 1: Identify components

  • a=4aa = 4a
  • b=bb = -b
  • n=3n = 3

The general term of the expansion is:

(3k)(4a)3k(b)k\binom{3}{k} (4a)^{3-k} (-b)^k


Step 2: Calculate each term

For k=0,1,2,3k = 0, 1, 2, 3:

  1. When k=0k = 0: (30)(4a)30(b)0=1(4a)31=64a3\binom{3}{0} (4a)^{3-0} (-b)^0 = 1 \cdot (4a)^3 \cdot 1 = 64a^3

  2. When k=1k = 1: (31)(4a)31(b)1=3(4a)2(b)=316a2(b)=48a2b\binom{3}{1} (4a)^{3-1} (-b)^1 = 3 \cdot (4a)^2 \cdot (-b) = 3 \cdot 16a^2 \cdot (-b) = -48a^2b

  3. When k=2k = 2: (32)(4a)32(b)2=3(4a)1b2=34ab2=12ab2\binom{3}{2} (4a)^{3-2} (-b)^2 = 3 \cdot (4a)^1 \cdot b^2 = 3 \cdot 4a \cdot b^2 = 12ab^2

  4. When k=3k = 3: (33)(4a)33(b)3=11(b)3=b3\binom{3}{3} (4a)^{3-3} (-b)^3 = 1 \cdot 1 \cdot (-b)^3 = -b^3


Step 3: Combine the terms

The expansion of (4ab)3(4a - b)^3 is:

64a348a2b+12ab2b364a^3 - 48a^2b + 12ab^2 - b^3


Step 4: Match the terms to the blanks

From the provided choices:

  1. 64a364a^3
  2. 48a2b-48a^2b48a2b48a^2b (negative sign is included)
  3. 12ab212ab^2
  4. b3-b^3

The correct arrangement is:

[ \text{[64a³]} - \text{[48a²b]} + \text{[12ab²]} - \text{[b³]} ]


Final Answer:

  • First box: 64a³
  • Second box: 48a²b
  • Third box: 12ab²
  • Fourth box:

Let me know if you'd like me to explain any step in more detail!


Related Questions:

  1. What is the binomial theorem, and how is it applied for powers of 4?
  2. How do you compute the binomial coefficients (nk)\binom{n}{k}?
  3. How do you expand a binomial with a negative term?
  4. What happens when the power nn increases in a binomial expansion?
  5. What is the relationship between Pascal's Triangle and the binomial theorem?

Tip: Always double-check the powers and coefficients of each term when expanding a binomial!

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Math Problem Analysis

Mathematical Concepts

Binomial Expansion
Algebraic Expressions

Formulas

Binomial Theorem: (a + b)^n = Σ [C(n, k) * a^(n-k) * b^k]

Theorems

Binomial Theorem

Suitable Grade Level

Grades 10-11