Does a straight angle have a vertex?

Question

I don't think it does.  The angle is labled K N X.

 

I also don't think it has any sides.  Am I correct?

Answer 1

Even though it is a straight angle, it can be named with three letters just like any other angle. In your example of straight angle KNX, point N would be the vertex and the sides would be NK and NX. All three points just happen to lie on line KX.

Answer 2

Oh yes!  Any point you choose.  They are all potential vertices.

What I mean is that since a line has an infinite number of points, they are all potential vertices.  In terms of your particular problem: A line is always defined (named) after 2 points on it.  An angle is always named after 3 points (the first letter represents a point on a ray, the middle point is the vertex, and the last letter is a point on the other ray).  So in your angle, the vertex is N.  But, since a straight angle is essentially a line, you can just pick 2 points to be on the rays and any point in-between these 2 points to represent a vertex (but there can only be one vertex for each angle you create).

I hope that makes sense.