Hello

I have a couple questions about graphs that I am not sure about...

1. If a graph contains a cycle that includes all the edges, the cycle is an Euler cycle. My answer: Yes, by the definition of the Euler cycle - a cycle in a graph G that includes

all of the edges and all of the vertices of G is called an Euler cycle.

2. Find a formula for the number of edges in Km,n . Answer: m*n. But not sure how to prove that...

3.Find a formula for the number of edges in Kn . Answer: (n(n-1))/2. But not sure how to prove that...

Thank you.