Five vertices.
Three
The vertex of a 3D pentagon is 10. :)
5
10 5 on the bottom and one for each vertex of the base connected to the vertex.
1 triangle is formed.
Pentagon
3 triangles
In a regular pentagon, the lines of symmetry are drawn from each vertex to the midpoint of the edge directly opposite the vertex, so there are five in all.
The lines inscribed as directed will result in a "star" being formed inside, and a pentagon will be formed in the middle of the star. The pentagram will have been separated into 11 regions by inscribing it as directed.
At most 5, since all symmetry lines must pass by a vertex. It has 5 if and only if the pentagon is regular.
1 vertex less than a hexagon is a pentagon. 2 angles more than a triangle is a pentagon.
5, one through each vertex, bi-secting the opposite side.