例: C & P82 B R & 解:(1)写表达式 M=AC·AB=AB N=BC·AB=ABC P=A.M.AB=A. ABC.AB=ABC.B=ABC=m4 Q=M·C·N A BC+ABC = m m7 R=AB.N·B= A BO例： P82 M 解: ⑴写表达式 C N PQR M = AC  AB = A BC N = BC  AB = ABC P = A M  AB = A A B C  AB = A B C  B = A B C = m4 Q = M C  N =  = A B C + ABC = m1 + m7 R = AB N  B =  = A B C = m2