It is easy to get OG=OH=OD= 1,

S△AEF = S△AEO+S△AOF = 1/2 * AE * OG+ 1/2 * AF * OH = 1/2 * OD *(AE+AF)= 7/2

②

F is the center of the square.

Let the side length be a, then DE=(√6-√2)*a/2 can be obtained.

DG=tg 15 *a=(2 - √3) *a

DE/DG==(√6+√2)/2