       Re: Coords of intersecting lines...

• To: mathgroup at smc.vnet.net
• Subject: [mg6371] [mg6371] Re: [mg5746] Coords of intersecting lines...
• From: Robert Pratt <rpratt at math.unc.edu>
• Date: Fri, 14 Mar 1997 14:54:03 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Perhaps I am missing something, but it seems that your problem is
ill-posed.  Given three points that lie on (unspecified) perpendicular
lines, one cannot necessarily determine the intersection point of the two
lines.  You must specify the lines.  For example, consider the three
vertices (a, b, and c) of an equilateral triangle.  If you choose any two of
these vertices (say a and b) to determine one of the lines, and take the
line through the third vertex (c) perpendicular to the first line, this
gives an intersection point that is the midpoint of a and b.  But if you
choose different pairs of perpendicular lines through a, b, and c, you
get different intersection points, namely the midpoints of a and c, and b
and c, respectively.

Rob Pratt
Department of Mathematics
The University of North Carolina at Chapel Hill
CB# 3250, 331 Phillips Hall
Chapel Hill, NC  27599-3250

rpratt at math.unc.edu

On Tue, 14 Jan 1997, Van der Poorten G. wrote:

> HI,
>
> I know this is a basic question, but after 15 years i tend to forget
> some things, specialy when you dont need math every day.
>
> Now, what am i looking for ?
>
> I'm trying to set up some equations on movement of cars and shock
> absorbers.( I'm actualy an 3D animator.)
> I got stuck with an over complicated formula when trying to find the
> intersectionpoint of 2 lines, only knowing 3 points a(x,y) b(x,y) c(x,y)
> and that both lines are perpendicular.
>
> Due to computation time, i must find the smallest formula possible.
>
> Can anyone help me on this?
>
> Btw, if you have information on automotive motion, plz let me know
>
>
>
> Van der Poorten Geert
> 3Digit
> Belgium
>
>

```

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