13 21b 2a23 c31b3a33 (6) 11a12a13 a21a22a2 a31a32a33 C 21a23 31a33b3 11a12a13 a21 22 23 a31a32a33， 31 32 33 21 22 23 11 12 13 31 3 33 21 2 23 11 1 13 2 a a a a a a a a a a b a a b a a b a x = . 31 32 33 21 22 23 11 12 13 31 33 3 21 23 2 11 13 1 3 a a a a a a a a a a a b a a b a a b x = (6) (7)