1。 Take A as the center of the circle and AB as the radius, and draw the extension line of the circle intersection DA at E..

2。 Determine the o point of DE by drawing with a ruler,

3。 With O as the center and OE as the radius, draw the extension line of circle intersection AB at F ..

4。 Make a square with side length AF.

It is proved that ∠ DFE = 90 because DE is the diameter.

In Rt△DEF

FA is higher on the hypotenuse, which is determined by the projective theorem.

FA^2=AE*AD=AB*AD

That is, AF is the square area with side length = rectangular ABCD area.