Triangles ABC and ABD are on the same base AB and between the same parallels AB and DC.
Therefore,
ar(ABD)=ar(ABC)
Subtract area of △AOB from both the sides.
ar(ABD)−ar(AOB)=ar(ABC)−ar(AOB)
⇒ar(AOD)=ar(BOC)
Diagonals AC and BD of a trapezium ABCD with AB ∥ DC intersect each other at O. Prove that ar (△AOD) = ar (△BOC). [1 MARK]