4 10 10 5 (5)E2=0 01 10 10 2 0 5/360 240 (6)B2-1=E2x=0 200 50 2 300 30 00 10 B2 (0,0,-120)1 2 32 1 2 32 4 2 1 0 1 0 10 5 5 1 (5) 0 1 0 1 10 2 1 1 0 0 0 0 10 10 2 1 0 5 360 240 1 (6) 0 1 200 50 2 300 30 1 0 0 10 (0,0, 120). B B E B E x C −     − −     = − = −       −             = = − =               = −