Have you ever studied Pythagorean Theorem? If you don't learn, this question is beyond the outline.

Answer: -2+5=3

So the coordinate of point B is (3,0).

According to Pythagorean theorem: OD 2 = AD 2-OA 2, the root number 3 of OD=2 is obtained, so the coordinate of point D is (0,2 root number 3).

Because DC=AB=5

So the coordinates of point C are (5,2 root numbers 3).

S=AB*OD=5*2 root number 3= 10 root number 3.