西安毛子科技大学XIDIANUNIVERSITY例4.B=(1,2,3)A=3(0/-1)AB=31美2BA =(1,2,3)= (1×1+2×2 +3×3)=(14)= 143例4． ( ) 1 2 , 1,2,3 3 A B   = =       ( ) 1 1 2 3 2 1,2,3 2 4 6 , 3 3 6 9 AB     = =             ( ) 1 1,2,3 2 3 BA   =       =  +  +  (1 1 2 2 3 3)= = (14) 14