Answer: x².
- A x²
- B x
- C 1
- D x³
Correct answer: A. x²
Explanation: (1-x)-1 = 1 + x + x2 + x3 + ... (infinite GP). The 3rd term is x2.
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