Answer: 10.
- A 5
- B 15
- C 20
- D 10
Correct answer: D. 10
Explanation: Coefficient of x<sup>3</sup> in (1+x)<sup>5</sup> is 5C3 = 10.
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