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

Practice Questions

Q1
In the expansion of (2 - x)^5, what is the coefficient of x^3?
  1. -80
  2. -60
  3. 60
  4. 80

Questions & Step-by-Step Solutions

In the expansion of (2 - x)^5, what is the coefficient of x^3?
  • Step 1: Identify the expression we are working with, which is (2 - x)^5.
  • Step 2: Recognize that we need to find the coefficient of x^3 in this expansion.
  • Step 3: Use the Binomial Theorem, which states that (a + b)^n = sum of (nCk * a^(n-k) * b^k) for k from 0 to n.
  • Step 4: In our case, a = 2, b = -x, and n = 5.
  • Step 5: We need to find the term where x is raised to the power of 3, which means we need k = 3.
  • Step 6: Calculate nCk, which is 5C3. This is the number of ways to choose 3 items from 5, calculated as 5! / (3! * (5-3)!).
  • Step 7: Calculate 5C3 = 5! / (3! * 2!) = (5 * 4) / (2 * 1) = 10.
  • Step 8: Now calculate 2^(n-k) = 2^(5-3) = 2^2 = 4.
  • Step 9: Next, calculate (-1)^k = (-1)^3 = -1.
  • Step 10: Combine these results to find the coefficient: 5C3 * 2^2 * (-1)^3 = 10 * 4 * (-1).
  • Step 11: Calculate the final result: 10 * 4 = 40, and then 40 * (-1) = -40.
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