Answer: 1120.
- A 1120
- B −1120
- C 560
- D 70
Correct answer: A. 1120
Explanation: With n = 8 the middle term is the 5th (r = 4): C(8,4)(2)⁴(−1)⁴ = 70·16 = 1120.
Row n of Pascal's triangle gives the coefficients nC0, nC1, ..., nCn for the expansion of (a+b)ⁿ; each number is the sum of the two numbers diagonally above it, a direct visual proof of the identity nCr = (n-1)C(r-1) + (n-1)Cr.
Concept context
Expansion of (a+b) n , general term, middle term, binomial coefficients, and greatest term