Answer: 20.
- A 10
- B 15
- C 20
- D 6
Correct answer: C. 20
Explanation: T(r+1) = 6Cr x6-r x-r = 6Cr x6-2r. For independent term: 6-2r=0, r=3. T4 = 6C3 = 20.
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