∠BOD =∠BAD +∠ABO
=1/2∠BAC +1/2∠AbC
=1/2(∠BAC+∠AbC )
=1/2(180°-∠ACB)
90°-1/2∠ACB
∠CoG=90°-∠BCO
=90°-1/2∠ACB
∠BOD =∠COG∠