Question

In any tree (with two or more vertices), there are at least two pendant vertices.

Answer 1

If T is a tree on two vertices, each of the vertices has degree 1. If T has at least three vertices it must have a vertex of degree k≥2, since otherwise 2(n−1)=∑ni=1di=n, which implies n=2. Hence it has at least k≥2 pendant vertices.