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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