Re: GeoGebra - bug report

[Geert Stappers <stappers@stappers.it>]

On Sun, Aug 23, 2015 at 02:02:12AM +0200, Walter Lenzenweger wrote:
> Dear Ladies and Gentlemen!
> 
> I have discovered two problems with the GeoGebra-command Tangent:
> 
> 1. By chance I acchieved to construct a tangent from a point which
> does NOT lie on the curve, but the parameter-options for the command
> Tangent
> only contain Tangent[Point on Curve, Curve]        (1)
> not Tangent[point, curve]!                        (2)
> 
> 2. While Tangent works for purpose (2), it does not work for purpose
> (1) - for implicit curves at least:
> 
> I have considered an implicit curve (algebraic curve, order 3), a
> point P in the plane and the tangent from P to c.
> 
> A = 1        B = 1        P=(-2,1)                c: A x³ + B y = 0
> t = Tangent[P,c]
> 
> I see 4 tangents to c through P, but if I change P to (0,0), save
> the file,reopen it, two windows appear saying: 'opening file failed'
> and a new ggb-window is opened but  I cannot open the saved file!
> 
> Of course it would be easy to solve this problem defining
> explicitely f(x) = -x^3 instead of c,
> but I am interested in tangents in given points of any algebraic
> curve which cannot be defined explicitely!
> 
> Best wishes and thanks for clearing this problem!
> 
> Walter Lenzenweger
> 
> P.S. I am using a Dell-notebook XPS L502X, Windows 7


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