Find nC1 12 + nC2 22 + nC3 32 + ... + nCn n2 (where nCr is the binomial coefficient).
Solution
Answer: n(n+1)2n-2.
Differentiate (1 + x)n, multiply by x and differentiate again. Set x = 1.
© John Scholes
jscholes@kalva.demon.co.uk
5 Feb 2002