Well, out of 10 questions I have two that are killing me. This proof is one of them. If someone could give me a push in the right direction I'd appreciate it.
"We suppose that we have n vertices in the Euclidean plane, and that we have used either the Kruskal or the Prim algorithm to draw the shortest network T among these vertices. Prove that whenever two edges of T meet at a vertex, the angle between them must be at least 60 degrees."
It's like the next question I'm going to post, I can visualize it, but have difficulty writing the proof.