In rectangular ABCD, it is known that ab = 3aD, e and F are two triad points of AB respectively, AC and DF intersect at point G Prove that EG is perpendicular to DF

In rectangular ABCD, it is known that ab = 3aD, e and F are two triad points of AB respectively, AC and DF intersect at point G Prove that EG is perpendicular to DF

And that. Proof?