-4x^(5m) y^(3m-n) /(-2x^(m+2n) y^(2m+n))
= 2x^(5m-m-2n) y^(3m-n-2m-n)
= 2x^(4m-2n) y^(m-2n)
上式与 -1/2x^6y^3是同类项,则 4m-2n =6,m-2n =3
解之,得 m=1,n= -1
所以 m^n = 1^(-1) = 1