。4.5??9??1.2 =4.5*(10-1)*1.2 =4.5*10*1.2-4.5*1*1.2 =45*1.2-4.5*1.2 =4.5*10*1.2-4.5*1.2 =4.5*(10*1.2-1.2) =4.5*(12-1.2) =4.5*10.8 =4.5*(10+0.8) =4.5*10+4.5*0.8 =45+3.6 =48.6
