Tangent plane in 3D

[toshk]

CAS; type
FZ1(x,y) enter
// gradient; numerical del operator
nDeriv(x^(1/3)*y^(1/3),{x,y}) enter;

//for Partial derivative do this instead
nDeriv(x^(1/3)*y^(1/3),x) enter;
nDeriv(Ans,y) enter;

save your appropriate ans(del or Partial your choice) in say FZ2; change x,y to X,Y iferr
do the steps...
doing this FZ2:= nDeriv(x^(1/3)*y^(1/3),{x,y}) enter; might not work;

applies to Function App too;