Original formula = lim (rou->; 0+)[( 1/(pai*(rou)^2))*e^((x 1)^2-(y 1)^2)*cos(x 1+y 1)*pai*(rou)^2]=lim(rou->; 0+)[e^((x 1)^2-(y 1)^2)*cos(x 1+y 1)]
Obviously when rou-& gt;; 0+,x 1->; 0,y 1->; 0, so the original formula = 1.