In the expansion of (x - 1)^5, what is the coefficient of x^3?

Practice Questions

Q1
In the expansion of (x - 1)^5, what is the coefficient of x^3?
  1. -10
  2. 10
  3. -5
  4. 5

Questions & Step-by-Step Solutions

In the expansion of (x - 1)^5, what is the coefficient of x^3?
  • Step 1: Identify the expression we are expanding, which is (x - 1)^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 = Σ [C(n, k) * a^(n-k) * b^k] for k = 0 to n.
  • Step 4: In our case, a = x, b = -1, and n = 5.
  • Step 5: We want the term where x is raised to the power of 3, which means we need k = 5 - 3 = 2.
  • Step 6: Calculate the binomial coefficient C(5, 2), which is the number of ways to choose 2 items from 5.
  • Step 7: C(5, 2) = 5! / (2! * (5-2)!) = 10.
  • Step 8: Since b = -1, we need to consider (-1)^2 for the term corresponding to k = 2.
  • Step 9: Calculate (-1)^2, which equals 1.
  • Step 10: Multiply the binomial coefficient by (-1)^2: 10 * 1 = 10.
  • Step 11: Therefore, the coefficient of x^3 in the expansion of (x - 1)^5 is 10.
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