9/8π

2。 Solution: Connect OD

OD ⊥AB

OC⊥AC

So OA divides CAD equally.

AD=AC=3

DB=5-3=2

Triangle ODB∽ triangle ACB

OD/DB=AC/BC

OD=3/2

S=(3/2) square *π* 1/2=9/8π.

If you have any questions, please ask.

Please adopt O(∩_∩)O~