Silly question?

[danielj]

(can you say why?)

From the free pdf, a Polygon is defined in Greek as ‘many-angle’, and with one straight line there are no angles or vertices, and with two straight lines there is one internal and one external. Also, one or two straight lines cannot define an area. Also, to try it out, I gave n a value of 1 and then 2 and in both cases it gives an answer of an internal angle of 0, which is nonsense I think?

I can understand your teaching, it just takes me awhile and several reads through to digest it, thank you. 
 

I understand reasonably well x,y and z axes, positive and negative as I have to occasionally use a laser cnc machine at work. I can visualise it.

[studiot]

Just now, danielj said:

I can understand your teaching, it just takes me awhile and several reads through to digest it, thank you.

I'm glad we are making progress.

Just now, danielj said:

From the free pdf, a Polygon is defined in Greek as ‘many-angle’, and with one straight line there are no angles or vertices, and with two straight lines there is one internal and one external. Also, one or two straight lines cannot define an area. Also, to try it out, I gave n a value of 1 and then 2 and in both cases it gives an answer of an internal angle of 0, which is nonsense I think?

A plane figure is the perimeter only of a shape that lies all in one plane (ie flat not like the surface of the Earth).

Such a shape may have any combination of curved or straight or straight sides, but it must be 'closed'. That is it must come back to its starting point and enclose some area, although the area does not form part of the figure.

The only closed shape with a single side is a circle  (note a circle is the perimeter only of a disc so it is the circle that has a circumference but no area and the disc that has the area).
 

A lens or lenticular has a two sided perimeter

Of course both lenses and circles have curved sides.

A polygon is a many sided figure, with all the sides straight.  (poly means many)

So a rectangle is a four sided figure.

If all the sides are the same length the figure is called a regular polygon and these are the sorts of figures we are considering.

There is more but that's the bare bones of it.