What is the coefficient of x^4 in the expansion of (x + 1)^8? (2020)

What is the coefficient of x^4 in the expansion of (x + 1)^8? (2020)

Step 1: Understand that we want to find the coefficient of x^4 in the expression (x + 1)^8.
Step 2: Recognize that (x + 1)^8 can be expanded using 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 = x, b = 1, and n = 8.
Step 4: We need to find the term where x is raised to the power of 4, which means we want the term where k = 4 (since x^(8-k) = x^4 when k = 4).
Step 5: Calculate C(8, 4), which is the number of ways to choose 4 items from 8. This is given by the formula C(n, k) = n! / (k! * (n-k)!).
Step 6: Plug in the values: C(8, 4) = 8! / (4! * (8-4)!) = 8! / (4! * 4!).
Step 7: Calculate 8! = 40320, 4! = 24, so C(8, 4) = 40320 / (24 * 24) = 40320 / 576 = 70.
Step 8: Therefore, the coefficient of x^4 in the expansion of (x + 1)^8 is 70.

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