Answer: 80.
- A 40
- B 160
- C 80
- D 10
Correct answer: C. 80
Explanation: T(r+1) = 5Cr x5-r 2r. For x2: 5-r=2, r=3. T4 = 5C3 x2 x 23 = 10 x 8 x x2 = 80x2. Coefficient = 80.
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