(2)、△<0 P(x, y)+p(x, yi=c ∫4=(x,y) 1n=∞2(x,y)0.8 1 0.6 0.4 0.2 0 x t 0 0.5 1 1.5 2 −1 −0.50 0.51 n 8 (2) 、   0 12 ( , ) ( , ) x y x y      =  = 1 2   ( , ) ( , ) x y x y i c  =