Homepage › Solution manuals › Gilbert Strang › Linear Algebra and Learning from Data › Exercise 5.1.11
m = 0p0+1p1+⋯+NpN = ∑ iipi = ∑ i ibi 2N = 1 2N ∑ iibi = 1 2N ∑ ii N! i!(N−i)! = 1 2N ∑ i N! (i−1)!(N−i)! = N 2N ∑ i (N−1)! (i−1)!(N−i)! = N 2N2N−1 = N 2