\(d(V_1F_1)+d(V_1F_2)=d(V_1F_2)+d(F_2V_2)=d(V_1V_2)=2a\)
\(d(V_2F_1)+d(V_2F_2)=d(V_2F_1)+d(F_1V_1)=d(V_2V_1)=2a\)
\(d(V_3F_1)+d(V_3F_2)=a+a=2a\)
\(d(V_4F_1)+d(V_4F_2)=a+a=2a\)
Furthermore, \(d(PF_1)+d(PF_2)=2a\) for every point \(P\) on the ellipse. This is the defining characteristic of an ellipse.