Express the following using only the terms A, 0 , The identity matrix I, and the number of nodes n: (a) A matrix N where Nij gives the number of common neighbors of vertices i and j. (b) An integer giving the total number of triangles in a network. A triangle is a set of three vertices, each of which are connected to both of the others. (c) The Laplacian of the complete network on n nodes (A network is complete if it has density 1).