Math Problem Statement

Find the terms containing x^2 in the expression (3x-1/2x)^8

Solution

To find the term containing x2x^2 in the expansion of (3x12x)8(3x - \frac{1}{2x})^8, we'll again use the Binomial Theorem.

Step 1: Binomial Theorem Formula

The Binomial Theorem states that: (a+b)n=k=0n(nk)ankbk(a + b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k In this case:

  • a=3xa = 3x
  • b=12xb = -\frac{1}{2x}
  • n=8n = 8

Step 2: General Term in the Expansion

The general term in the expansion is given by: Tk+1=(8k)(3x)8k(12x)kT_{k+1} = \binom{8}{k} (3x)^{8-k} \left(-\frac{1}{2x}\right)^k

Step 3: Simplify the General Term

Simplifying Tk+1T_{k+1}: Tk+1=(8k)(3x)8k(12x)kT_{k+1} = \binom{8}{k} \cdot (3x)^{8-k} \cdot \left(-\frac{1}{2x}\right)^k Tk+1=(8k)38kx8k(1)k2kxkT_{k+1} = \binom{8}{k} \cdot 3^{8-k} \cdot x^{8-k} \cdot \frac{(-1)^k}{2^k} \cdot x^{-k} Tk+1=(8k)38k(1)k2kx8kkT_{k+1} = \binom{8}{k} \cdot \frac{3^{8-k} \cdot (-1)^k}{2^k} \cdot x^{8-k-k} Tk+1=(8k)38k(1)k2kx82kT_{k+1} = \binom{8}{k} \cdot \frac{3^{8-k} \cdot (-1)^k}{2^k} \cdot x^{8-2k}

Step 4: Find the Value of kk for x2x^2

To find the term containing x2x^2, set the exponent of xx equal to 2: 82k=28 - 2k = 2 Solve for kk: 82k=28 - 2k = 2 2k=62k = 6 k=3k = 3

Step 5: Substitute k=3k = 3 into the General Term

Now substitute k=3k = 3 back into the general term: T4=(83)383(1)323x2T_{4} = \binom{8}{3} \cdot \frac{3^{8-3} \cdot (-1)^3}{2^3} \cdot x^2 T4=(83)35(1)8x2T_{4} = \binom{8}{3} \cdot \frac{3^5 \cdot (-1)}{8} \cdot x^2 T4=8×7×63×2×1243(1)8x2T_{4} = \frac{8 \times 7 \times 6}{3 \times 2 \times 1} \cdot \frac{243 \cdot (-1)}{8} \cdot x^2 T4=562438x2T_{4} = 56 \cdot \frac{-243}{8} \cdot x^2 T4=1701x2T_{4} = -1701x^2

Final Answer

The term containing x2x^2 in the expansion of (3x12x)8(3x - \frac{1}{2x})^8 is: 1701x2-1701x^2

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Related Questions:

  1. How do you find the coefficient of a specific term in a binomial expansion?
  2. What is the term containing x4x^4 in this expansion?
  3. How would the expansion change if the exponent were a different value?
  4. What are the first and last terms in the expansion?
  5. Can you identify a pattern in the coefficients of terms in the binomial expansion?

Tip: When dealing with binomial expansions that involve fractions or negative terms, pay close attention to how these factors influence the coefficients and the signs of each term.

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Math Problem Analysis

Mathematical Concepts

Binomial Theorem
Binomial Expansion
Combinatorics

Formulas

Binomial Theorem

Theorems

Binomial Theorem

Suitable Grade Level

High School