Stephen <mca### [at] aolcom> wrote:
> On 12/02/2013 8:22 PM, Christian Froeschlin wrote:
> > Stephen wrote:
> >
> >>> Since you are dealing with lines in 3-space (x,y,z), the lines will only
> >>> intersect if they lie on the same plane.
> >
> >> Can that be right?
> >
> > take two pens, and you will find you can easily hold them
> > so that they do not intersect, are not parallel, and with the
> > point of closest approach clearly within the physical pen
> > boundaries (and not just their projection to infinity).
> >
>
> Yes, that is true.
>
> >> What about the lines of the three axis?
> >
> > any two axes lie within a plane and intersect at the origin.
>
> And is the third axis, in 3D space, in the same plane as the plane of
> the first two axis?
>
>
> --
> Regards
>      Stephen

The x & y axis intersect because they are both on the same plane (x-y plane with
z as the normal), similar for the y & z and x & z.  So yes they are co-planar.

-tgq

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