ˆˆˆˆVCV ˆVˆC ˆ(1)CCI ˆˆVC V 1 2 []1E 2 2ˆ 22ln()ntntntQzz ˆ/ntntntzr ˆ()Q()Q ˆ()()Q QQˆˆˆˆ ˆ 221 []A B C22(1)21ttAx21ttBy2(1)tttCx y22224242221[][]222222]EABCABACABCBC22221[][]ttttE AE x x 2222[][] []ttttE x xE xE x22[]1ttE x x4[]1tE x22[]1 2ttttE x x 221[](12)ttttE A221[](2)tE A22[]E A22[]E B24(1)2[][]2E CE x y xyt t ttt t 21tttyx ttx 22[]1 2ttttE x x2[]tttE x xt[]tt ttE xx2222[][] []1ttttE xE xE 2tytyt 20aa 2ˆ2ˆ/z r 22ln()Qzz 22[]E r ˆ ˆ 22 []E Q24 ˆ()()Q QQ2222[]ln()1ˆˆEQ222ˆ1[]ln(1)11EQ2[]2EQ []1.61E Q[]0.26E Q