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Topic: geometry help
Replies: 8   Last Post: Apr 26, 2014 11:56 AM

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Posts: 359
Registered: 9/16/06
Re: geometry help
Posted: Apr 26, 2014 12:06 AM
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> For a parabola b^2-4ac = 0 so B^2 = 4 AC
> If B=0 then either A or C = 0
> So the equation becomes either
> C.Y^2 + D.X + E.Y + F = 0 with axis // oX, or
> A.X^2 + D.X + E.Y + F = 0 with axis // oY
> In either case 4 points are necessary to determine
> the equation...

Hi Peter!

Without loss of genearlty we can divide out the above by F so that there remain three constants only.
Accordingly, three points only need to be given to determine a parabola parallel to either oX or oY, as:
y = a x^2 + b x + c and x = A y^2 + B y + C.

An inclined axis needs one more constant or one more point.

Best Regards

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