A relation is a function when 2 or more of the domain are the same, if none are the same then it is a function.
Get tan to be sin/cos then eliminate the sins and cos that correspond
Vertices are formed when 2 sides come together on a polygon. So they are basically corners. The smallest amount of sides a polygon has is 3, which would be a triangle. And triangles have 3 corners, because with a triangle, each side touches the other two. So the minimum number of vertices needed to form a polygon would be 3.