L=.(a,+bx+cy) 2△ (a; +b,x+cy) MPik △Pjk 2△ (ak+bx+cky) △Pii 2A 2△ k k k x Yk ill (a; +b,x+cy i,jk=1,2,3 2△ ai=x yk-yj* b=y,-yk ci x:+j i k y x P Pij Pik Pjk ( y) 2 1 i i i i L a + b x + c  = i j k j k a = x y − y x i j k b = y − y i j k c = −x + x i, j, k =1,2,3 ( y) 2 1 i i i i L a + b x + c  = ( y) 2 1 j j j j L a + b x + c  = ( y) 2 1 k k k k L a + b x + c  =                      =           y x a b c a b c a b c L L L k k k j j j i i i k j i 1 2 1                     =           k j i i j k i j k L L L y y y x x x y x 1 1 1 1