Let P = {Xo, X1, X2, ... ., x} be a regular partition of the interval [0, b], and set f (x) = x. Show that: b2 Lf(P) = 2 0 + 1+ 2+ ... + (n-1)] And b2 Uf(P) = n2 [1 + 2 + 3 + ... + n]