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# simple problem

Mark gatfix at hotmail.com
Thu May 18 07:17:01 EST 2000

```In article <39232CD6.23DE8D21 at compuserve.com>,
"M. Johan Broekman" <hanbroekman at compuserve.com> wrote:
> Mark wrote:
> >
> > Given the cartesian coordinates of
> > two points a and b in 3D space, I need the position
> > of a third point c such that the angle c-a-b has a fixed
> > value, say 104.5 degrees.
> >
> >           c
> >            \
> >             a - b
> >
> > how can I obtain the coordinates (x,y,z) of c from the
> > known coordinates of a and b?
> > Clearly there are many equivalent choices of c satisfying
> > this requirement; what I'm looking for is simply the direction of
some
> > a-c axis which form the required angle with the a-b axis.
> >
> > is it a trivial problem? I haven't found a solution...
> > any help appreciated
> >
> > Sent via Deja.com http://www.deja.com/
>
> My very old, and rudimentary trig experiences suggest that there are
an
> infinite number of points "c", all laying on a cone shaped surface
with
> angle xyz from the line a-b.
> --
> Best regards
> Han Broekman

Of course; what I need is an expression that, starting from the
direction of the AB axis, provides a generic point xyz
laying on such cone surface.
best regards
mark

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