What is the coefficient of x^2 in the expansion of (3x + 4)^5?

Practice Questions

Q1
What is the coefficient of x^2 in the expansion of (3x + 4)^5?
  1. 60
  2. 80
  3. 100
  4. 120

Questions & Step-by-Step Solutions

What is the coefficient of x^2 in the expansion of (3x + 4)^5?
  • Step 1: Identify the expression we need to expand, which is (3x + 4)^5.
  • Step 2: Recognize that we want the coefficient of x^2 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 = 3x, b = 4, and n = 5.
  • Step 5: We need to find the term where the power of x is 2. This happens when we choose (3x) twice (which gives us x^2) and (4) three times.
  • Step 6: Calculate the number of ways to choose 2 from 5, which is C(5, 2). C(5, 2) = 5! / (2!(5-2)!) = 10.
  • Step 7: Calculate (3)^2, which is 9.
  • Step 8: Calculate (4)^3, which is 64.
  • Step 9: Multiply these values together: C(5, 2) * (3)^2 * (4)^3 = 10 * 9 * 64.
  • Step 10: Perform the multiplication: 10 * 9 = 90, and then 90 * 64 = 5760.
  • Step 11: Conclude that the coefficient of x^2 in the expansion of (3x + 4)^5 is 5760.
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