What is the 5th term in the expansion of (2x - 3)^7?

Practice Questions

Q1
What is the 5th term in the expansion of (2x - 3)^7?
  1. -1134x^5
  2. 1134x^5
  3. -1458x^5
  4. 1458x^5

Questions & Step-by-Step Solutions

What is the 5th term in the expansion of (2x - 3)^7?
  • Step 1: Identify the expression to expand, which is (2x - 3)^7.
  • 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 = 2x, b = -3, and n = 7.
  • Step 4: We want the 5th term in the expansion. The 5th term corresponds to k = 4 (since we start counting from k = 0).
  • Step 5: Calculate the binomial coefficient C(7, 4), which is the number of ways to choose 4 items from 7. C(7, 4) = 7! / (4! * (7-4)!) = 35.
  • Step 6: Calculate (2x)^(7-4) = (2x)^3 = 8x^3.
  • Step 7: Calculate (-3)^4 = 81.
  • Step 8: Combine these results to find the 5th term: C(7, 4) * (2x)^3 * (-3)^4 = 35 * 8x^3 * 81.
  • Step 9: Multiply the coefficients: 35 * 8 * 81 = 22680.
  • Step 10: The 5th term is 22680x^3.
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