∫ quadrilateral ABDE is a square,

∴∠AOB=90，OA=OB，

∴∠AOM+∠BOF=90，

∠ amo = 90。

∴∠AOM+∠OAM=90，

∴∠BOF=∠OAM，

At △AOM and △BOF,

AMO=∠OFB=90 degrees

∠OAM=∠BOF

OA=OB，

∴△AOM≌△BOF(AAS)，

∴AM=OF,OM=FB，

∠ ACB =∠ AMF =∠ CFM = 90，

∴ Quadrilateral ACFM is rectangular,

∴AM=CF,AC=MF=5，

∴OF=CF，

∴△OCF is an isosceles right triangle,

∫CF = OF = BC-FB = BC-OM = BC-(OF-AC)= 9-OF+5 = 14-OF

Then 2CF= 14, CF=OF=7.

Pythagorean Theorem: OC? =2OF？

OC=√2？ OF=7√2