We let h equal the little distance from the top of the bottom square to the
center of the circle.

The two red lines marked r are radii.

There are two right triangles, and their hypotenuses are the
radii, of length r.

Applying the Pythagorean theorem to the upper right triangle:





Applying the Pythagorean theorem to the lower right triangle:





We set the two expressions for r2 equal:



Subtract h2 from both sides:







We substitute h=3 in






The area of a circle is



So the area of the circle is

   <--answer

Edwin