Calculate the coefficient of x^4 in the expansion of (3x - 2)^6.

Practice Questions

Q1
Calculate the coefficient of x^4 in the expansion of (3x - 2)^6.
  1. 540
  2. 720
  3. 810
  4. 960

Questions & Step-by-Step Solutions

Calculate the coefficient of x^4 in the expansion of (3x - 2)^6.
  • Step 1: Identify the expression to expand, which is (3x - 2)^6.
  • Step 2: Use the Binomial Theorem, which states that (a + b)^n = Σ [C(n, k) * a^(n-k) * b^k] for k = 0 to n.
  • Step 3: In our case, a = 3x, b = -2, and n = 6.
  • Step 4: We want the coefficient of x^4, which means we need the term where (3x) is raised to the power of 4.
  • Step 5: This occurs when k = 2 because (n - k) = 4, so k = 6 - 4 = 2.
  • Step 6: Calculate C(6, 2), which is the number of ways to choose 2 from 6. C(6, 2) = 6! / (2!(6-2)!) = 15.
  • Step 7: Calculate (3)^4, which is 3 raised to the power of 4. (3)^4 = 81.
  • Step 8: Calculate (-2)^2, which is -2 raised to the power of 2. (-2)^2 = 4.
  • Step 9: Multiply the results: Coefficient = C(6, 2) * (3)^4 * (-2)^2 = 15 * 81 * 4.
  • Step 10: Calculate 15 * 81 = 1215, then multiply by 4 to get 4860.
  • Binomial Theorem – The Binomial Theorem provides a way to expand expressions of the form (a + b)^n, where the coefficients can be calculated using combinations.
  • Combinations – Understanding how to calculate combinations (C(n, k)) is essential for determining the coefficients in the binomial expansion.
  • Exponent Rules – Applying exponent rules correctly when calculating powers of terms in the expansion.
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