Find the limit, if it exists. (If an answer does not exist, enter DNE.) lim(x,y)(0,0)x2+y2+648x2+y2 Determine the set of points at which the function is continuous. f(x,y)={4x2+y2x2y31if(x,y)=(0,0)if(x,y)=(0,0) {(x,y)xR and y=0} {(x,y)(x,y)=(0,0)} {(x,y)xR and yR} {(x,y)x>0 and y>0} {(x,y)xy=0}