2m-4n=82m-n=3-3n=5n=-5/3m=2/3m+n=-1
m+2n=4m=4-2n2(4-2n)-n=38-5n=3n=1,2m-1=3m=2.
是m-n吧
则m=n的值是!!m=n???啥意思???