例2 b3) a3b, a3b2 a3b3 a,6+a262+a3b3例2 ( ) 1 2 3 3 2 1 b b b a a a                     = 3 1 3 2 3 3 2 1 2 2 2 3 1 1 1 2 1 3 a b a b a b a b a b a b a b a b a b ( )           3 2 1 1 2 3 a a a b b b = a1b1 + a2b2 + a3b3