Let Dn denote the space of all functions from the set {1, 2, 3,..., n} to IR

Question:

Let Dn denote the space of all functions from the set {1, 2, 3,..., n} to IR with point-wise addition and scalar multiplication (see Exercise 35 §6.3). Show that (,) is an inner product on Dn
if (f ∙ g) = f(1)g(D + f(2)g(2) +∙∙∙∙∙∙∙∙∙+ f(n)g(n)