(m^2+n^2)(m^2+n^2-9)-10=0,
则(m^2+n^2)^2-9(m^2+n^2)-10=0,
∴(m^2+n^2+1)(m^2+n^2-10)=0,m^2+n^2+1>0,
∴m^2+n^2=10.