Answer: 15.
- A 15
- B −15
- C 20
- D 6
Correct answer: A. 15
Explanation: General term power is 12 − 3r; independent when r = 4, giving C(6,4)(−1)⁴ = 15.
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