BO=OD
Since BO=OD is the mid point
we know thta a mid point of a △ divides it into two △ of equal areas
CO is medpoint of △BCD
i.e., ar(△COD)=ar(△COB)−−−(1)
AO is a medpoint of △ABD
i.e. ar(△AOD)=ar(△AOB)−−−(2)
from (I) & (II) we have
ar(△COD)+ar(△AOD)=ar(△COB)+ar(△AOB)
ar(△ADC)=ar(△ABC)