3) IJ = IA + AB + BJ
IJ = -AI + AB + BJ
IJ = -(1/2) AB + AB + 2 BA
IJ = -(1/2) AB + AB - 2 AB = -(3/2) AB
4) LK = LC + CK = - CL + CK = - ( 2/3 BC - 13/6 AB ) + ( - 2/3 CA )
LK = - (2/3) ( BC + CA ) + 13/6 AB
BC + CA = BA
LK = - (2/3) BA + (13/6) AB
LK = 2/3 AB + 13/6 AB = 4/6 AB + 13/6 AB = 17/6 AB