3x+2y=m+3 式12x-y=2m-1 式2由式1加上式2乘以2得3x+4x=m+3+4m-2解得 x=(5m+1)/7由式1乘以2减去式2乘以3得4y+3y=2m+6-6m+3解得 y=(9-4m)/7由题目有 x+y=0 即 (5m+1)/7+(9-4m)/7=0得 5m+1+9-4m=0解得 m=-10...