(2) P.(G2)=k(k-1(k-2k-3)+2k(k-1k-2)+k(k-1) =k(k-1)K2-3k+3) 80.8 1 0.6 0.4 0.2 0 x t 0 0.5 1 1.5 2 1 0.5 0 0.5 1 n 8 (2) G2 2 2 ( ) ( 1)( 2)( 3) 2 ( 1)( 2) ( 1) ( 1)( 3 3) PG kk k k kk k kk k kk k k          