In the expansion of (2x - 3)^5, what is the coefficient of x^4?

Practice Questions

Q1
In the expansion of (2x - 3)^5, what is the coefficient of x^4?
  1. -90
  2. -120
  3. -150
  4. -180

Questions & Step-by-Step Solutions

In the expansion of (2x - 3)^5, what is the coefficient of x^4?
Correct Answer: -240
  • Step 1: Identify the expression we are expanding, which is (2x - 3)^5.
  • Step 2: Recognize that we need to find the coefficient of x^4 in this expansion.
  • Step 3: 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 4: In our case, a = 2x, b = -3, and n = 5.
  • Step 5: We want the term where the power of x is 4. This happens when k = 1 (because 5 - k = 4).
  • Step 6: Calculate C(5, 1), which is the number of ways to choose 1 from 5. C(5, 1) = 5.
  • Step 7: Calculate (2)^4, which is 16.
  • Step 8: Calculate (-3)^1, which is -3.
  • Step 9: Multiply these values together: 5 (from C(5, 1)) * 16 (from (2)^4) * (-3) (from (-3)^1).
  • Step 10: Perform the multiplication: 5 * 16 = 80, and then 80 * (-3) = -240.
  • Step 11: Conclude that the coefficient of x^4 in the expansion of (2x - 3)^5 is -240.
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