O is any point on the diagonal PR of a parallelogram PQRS . prove that ar(PSO) = ar(PQO) .
draw AS and BQ pependiculars on PR from S and Q resp.
then AS= BQ (peependiculars drawn from opp. verices of a IIgm are equal)
thus ar of POS= 1/2*PO*AS & ar of PQO= 1/2*PO*BQ but as AS= BQ hence ar of 2 tri. are equal