Find the local maximum and minimum values and saddle point(s) of the function. If you have three-dimensional graphing software, graph the function with a domain and viewpoint that reveal all the important aspects of the function. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)

f(x,y) =3x³9x+9xy²

local maximum value(s)

local minimum value(s)

saddle point(s)(x,y,f) =