It is given that ∠OFB=∠OFD.
Draw OP⊥AB and OQ⊥CD.
In ΔOFP and ΔOFQ,
FO=FO(common)
∠FPO=∠FQO(each90∘)
∠OFB=∠OFD(given)
So, by AAS criteria, ΔOFP≅ΔOFQ.
By CPCT, OP=OQ
Since, the chords equidistant from the centre are equal in length, then,
AB=CD