lg x=lg(m+r)+lg(m^2−mr+r^2)
Lgx= lg( m+ r)(m^2- mr+ r^2) x=( m+ r)( m^2- mr+r^2) x=m^3- r^3
x>0 m^3-r^3>0 m^3> r^3 m> r
x>0 m^3-r^3>0 m^3> r^3 m>r