Question 15 Diagonals AC and BD of a quadrilateral ABCD intersect at O in such a way that ar(AOD) = ar(BOC). Prove that ABCD is a trapezium.
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Solution
It is given that, Area(ΔAOD)=Area(ΔBOC) Area(ΔAOD)+Area(ΔAOB)=Area(ΔBOC)+Area(ΔAOB) [Adding Area (ΔAOB) to both sides] Area(ΔADB)=Area(ΔACB)
We know that triangles on the same base having areas equal to each other lie
between the same parallels.
Therefore, these triangles, ΔADB and ΔACB, are lying between the same parallels.
i.e., AB || CD
Therefore, ABCD is a trapezium.