9 spots

Originally posted by Thomaster
Your cilinder trick doesn't work, since the line should remain straight. (what is impoosible on a rolled paper)

I think I understand how you do it with one line. You take two papers.
First you hit three dots with a straight line and you 'park' the line in the second paper. You can simply move the dots :-)

The surface of a paper is two-dimensional even if it's bent. On this two-dimensional paper the line is straight. If you don't accept this, then it's impossible to go straight west on the surface of the earth.
But never mind, this is not my solution, I don't defend it.

If your solution is correct then there are another solution as well.

Originally posted by FabianFnas
The surface of a paper is two-dimensional even if it's bent. On this two-dimensional paper the line is straight. If you don't accept this, then it's impossible to go straight west on the surface of the earth.
But never mind, this is not my solution, I don't defend it.

If your solution is correct then there are another solution as well.

Don't underestimate cilinders, even those things are 3D. And yes, the earth isn't straight either.

owow, did you just say there is another solution, because mine is correct? 😕

Originally posted by Thomaster
Don't underestimate cilinders, even those things are 3D. And yes, the earth isn't straight either.

owow, did you just say there is another solution, because mine is correct? 😕

Every point of the surface of a cylindre demands two coordinates, and no more, two is enough, therefore the surface of a cylindre is two-dimensional.
Even the surface of the Earth is two-dimensional of the same reason, two coordinates is enough.
But never mind if you disqualify this solution, there is another one.

Originally posted by FabianFnas
Every point of the surface of a cylindre demands two coordinates, and no more, two is enough, therefore the surface of a cylindre is two-dimensional.
Even the surface of the Earth is two-dimensional of the same reason, two coordinates is enough.
But never mind if you disqualify this solution, there is another one.

Just two coordinates? Do you use a round axis? 😛

you can have straight lines on a curved surface, eg any line of longitude or latitude. Coordinates can be given in latitude and longitude as well, which is one coordinate system.

I still cannot see the other one line solution, is it a sort of kick yourself when you see it one?

Originally posted by Thomaster
Just two coordinates? Do you use a round axis? 😛

Originally posted by deriver69
you can have straight lines on a curved surface, eg any line of longitude or latitude. Coordinates can be given in latitude and longitude as well, which is one coordinate system.

I still cannot see the other one line solution, is it a sort of kick yourself when you see it one?

Every point on the surface of a cylindre can be described woth two coordinates: (1) The distance from some defined midpoint (or end-point) on the surface and (2) how many degrees around the surface, in degrees or radians. Two coordinates is enough. But there is an interior too, for that it takes a third coordinate, but we can only draw a line on it's surface so two is enough.

I give a clue of 'my' solution. I worked at a supermarket once, and they thought I was pretty clever with drawing posters, you know "For sale - chicken - half price!". I got the idea for the solution then...

Originally posted by FabianFnas
Every point on the surface of a cylindre can be described woth two coordinates.

http://www.mostert.org/3dindepraktijk/afbeeldingen/h3/as1.gif

Paint your cylindre in this and try to describe a point with just two coordinates.

Originally posted by Thomaster
http://www.mostert.org/3dindepraktijk/afbeeldingen/h3/as1.gif

Paint your cylindre in this and try to describe a point with just two coordinates.

There are points on the surface of the cylinder (those are interesting), and there are points not on the surface of the cylindre (the other are not interesting).

Let skip the cylindre for a while and go to the surface of the earth, and we assume the surface is smooth as a sphere. Okay? Now, you are somewhere on this globe. How many coordinates does it take to fully describe your position on the surface of the globe? Latitude and longitude. If you tell me your latitude and longitude of your home location, and I know where your live. Two is enough, three is not neccesary. Right?

Let's go back to the cylindre. Take a flat map over the world in paper. Make a roll out of it. It's cylindrical. You can thus represent every point on this cylindrical map and give two coordinates for every point, latitude and longitude. Two is enough.

But this is beyond the point of the problem given. I can cover 9 points with one straight stroke only of a marker pen. That's the solution. How do I do that?

Are you allowed to cut up the paper?

Originally posted by Habeascorp
Are you allowed to cut up the paper?

You ask me? I don't know, I didn't do it...

Originally posted by FabianFnas
I give a clue of 'my' solution. I worked at a supermarket once, and they thought I was pretty clever with drawing posters, you know "For sale - chicken - half price!". I got the idea for the solution then...

Is this a hint?: At that work I used a broad marker pen.

Originally posted by FabianFnas
Is this a hint?: At that work I used a broad marker pen.

My solution to the problem - 9 points, one straight line:

Use a marker pen with a broad tip so you can cover nine points in one single stroke.