∴.AX3=E,AX4=0, BX=0,BX2=E2 .X3=A,X4=0,X=0,X2=B 8- 1 1 3 4 1 2 X A X X X B , 0, 0, − −  = = = = 1 1 1 0 0 0 0 A B B A − − −      =         3 1 4 1 2 2 , 0, 0, AX E AX BX BX E  = = = =