[futurebasic] Re: Coordinate geometry.

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From: Chris <behmc@...>
Date: Thu, 11 Dec 1997 09:08:59 -0500
>Does anyone know the answer to these two geometry questions?
>1. The formula for finding the intersection point of two lines.
>2. Given the coordinates of three points that lie on the arc of a circle,
>how do you find the radius and centre of that circle.
>I have the source code for the first in C, but of course it is complete
>gibberish. Even the basic maths formula is complete gibberish, and cannot
>be written in ASCII... at least by me.
>Its not really my excuse that I am Australian, lazy and or thick although
>any or all of these may be true. Also I have no control over Lazlo Toth
>or what he says.

The intersection point of two lines is found by setting the two line
equations equal to each other, solving for x and then substituting that
value into one of the original equations to find y.


y1 = 3x + 2
y2 = -4x

Find x where they intersect

3x + 2 = -4x
     2 = -7x
  -2/7 = x

So at the x coordinate -2/7 the lines will intersect.

y1 = 3x + 2
y1 = 3(-2/7) + 2
y1 = -6/7 + 2
y1 = 8/7

So the point where they cross is (-2/7,8/7).

I haven't ever tried (or wanted to try) to do the actual formula in BASIC
(or any language) so I won't attempt it here - hopefully though you can see
what needs to be done (and maybe how to convert it from C) by this example.