GEOMETRICAL PUZZLE - IV

Here is a geometrical puzzle of highschool level. Try to solve it.

There is a semicircular plot of land with radius R. A square garden is to be prepared in this semicircular region such that two vertices of the square are on the semicircular arc and remaining two vertices are on the diameter. What will be the area of the square in terms of radius R ?

If you get the answer then place it as a comment to my post. You require a Google registration for that. I will post the answer with solution on August 12.