Question 9 In figure X and Y are the mid - points of AC and AB respectively, QP || BC and CYQ and BXP are straight lines. Prove that ar(ΔABP)=ar(ΔACQ).
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Solution
Since X and Y are the midpoints of AC and AB respectively, XY || BC We know that triangle on the same base and between the same parallels are equal in area. Here, ΔBYC and ΔBXC lie on same base BC an between the same parallels BC and XY. So, ar(ΔBYC)=ar(ΔBXC) On subtracting ar(ΔBOC) from both sides, we get ar(ΔBYC)−ar(ΔBOC)=ar(ΔBXC)−ar(ΔBOC) ⇒ar(ΔBOY)=ar(ΔCOX) On adding ar(ΔXOY) both sides, we get ar(ΔBOY)+ar(ΔXOY)=ar(ΔCOX)+ar(ΔXOY) ar(ΔBYX)=ar(ΔCXY) ...(i) Hence, we observe that quadrilaterals XYAP and YXAQ are on the same base XY and between the same parallels XY and PQ. ∴ar(XYAP) = ar (YXAQ) ....(ii) On adding eqs. (i) and (ii), we get, ar(ΔBYX)+ar(XYAP)=ar(ΔCXY)+ar(YXAQ) ⇒ar(ΔABP)=ar(ΔACQ)