m+n=3，m-n=2解得m=5/2，n=1/2所以m^2+n^=13/2mn=5/4m+n=3，m-n=2两式左右相加得 (m+n)+(m-n)=3+2,即2m=5,m=5/2m=5/2代入得5/2+n=3,即n=1/2
