problem with partial derivative
In the attached GGB file I define a function a(x,y) to give the total distance of the point (x,y) from three points A,B and C.
I would like to find the partial derivatives of a(x,y) with respect to x and also with respect to y. Geogebra calculates these, but I do not understand the resulting b(x,y) and c(x,y).
Geogebra understands a(x,y) as a proper two-variable function, and can calculate the values, but it does not understand b(x,y) as a two-variable function, it for example gives b(0,0) undefined.
I guess, I can redefine a(x,y) differently, but I am not sure if this is a bug or not in the partial derivative algorithm.