The equation ax2+bx+c=0 ; a,b,c  ∈  Q,  a≠0,  has rational roots if

The given equation ax2+bx+c=0 ; Here a,b,c  ∈  Q,  a≠0, Given that roots are rational,So, by the condition :For rational roots, discriminant should be a perfect square of a rational number. ∴ b2−4ac  is the perfect square of a rational number.