x+y=5m+2 ......(1)x-y=4m-5 ......(2) (1)+(2)得：2x=9m-3 (1)-(2)得：2y=m+7 3x+y=66x+2y=123*2x+2y=123(9m-3)+(m-7)=1227m-9+m-7=1228m-16=1228m=28m=1
