00:01
Okay, so a spanning tree of a simple graph g is a subgraph of g that is a tree containing every vertex of g.
00:11
So for part a, we have, well, k sub3.
00:19
So this is equal to what we have here, we have vertex.
00:25
This is vertex a, and then we have vertex b.
00:31
And vertex c, which is connected back to vertex a.
00:37
Okay, so what are the spanning trees here of k -sub -3? well, there are three, right? we have, first, we have the spanning tree, we have a, which goes to b, and then which goes to c.
00:58
Or we have a, which goes to, c and then which goes back here to b or we have a which goes down to b and then which connects over here to c.
01:27
So therefore k 3 has three has three different or distinct spanning trees.
01:45
All right so case three has three okay so that is part a and then looking at part b while we have k sub four so this is equal to we have um well our vertex a b c d okay and then we connect on the diagonals like this okay so here right we see that while we see that while he's betting tree of k -sup -4 contains three edges.
02:28
And there are six edges, right, in k -sup -4.
02:33
So a total number of combinations here of three edges from among the six edges, while we have that k -sup -4 is equal to six times c -3, which is equal to to, well, six over three, three, which is equal to 20.
03:09
Okay...