(a^m)^n=a^6,(a^m)/a^n=a^3,a>0,a≠1(改题了)所以mn=6,①m-n=3,m=n+3,②把②代入①，n^2+3n-6=0,解得n1=(-3+√33)/2,n2=(-3-√33)/2.代入②，m1=(3+√33)/2,m2=(3-√33)/2.所以4m^2+n^2=3m^2+(m-n)^2+2mn=3(21土3√3)/2+9+12=(105土9√3)/2.
