The side $ \mathrm{AB} $ of a parallelogram $ \mathrm{ABCD} $ is produced to any point $ \mathrm{P} $. A line through $ \mathrm{A} $ and parallel to $ \mathrm{CP} $ meets $ C B $ produced at $ Q $ and then parallelogram PBQR is completed (see figure below). Show that $ \operatorname{ar}(\mathrm{ABCD})=\operatorname{ar}(\mathrm{PBQR}) $. [Hint : Join $ \mathrm{AC} $ and $ \mathrm{PQ} $. Now compare ar (ACQ) "
Given:
The side \( \mathrm{AB} \) of a parallelogram \( \mathrm{ABCD} \) is produced to any point \( \mathrm{P} \). A line through \( \mathrm{A} \) and parallel to \( \mathrm{CP} \) meets \( C B \) produced at \( Q \) and then parallelogram PBQR is completed.
To do:
We have to show that \( \operatorname{ar}(\mathrm{ABCD})=\operatorname{ar}(\mathrm{PBQR}) \).
Solution:
Join $AC$ and $PQ$.
$PQ$ and $AC$ are diagonals of parallelograms $PBQR$ and $ABCD$ respectively.
Therefore,
We know that,
Diagonal of a parallelogram divides it into two triangles of equal area.
This implies,
$\operatorname{ar}(\triangle \mathrm{ABC})=\frac{1}{2} \operatorname{ar}(\mathrm{ABCD})$......(i)
$\operatorname{ar}(\mathrm{\triangle PBQ})=\frac{1}{2} \operatorname{ar}(\mathrm{PBQR})$........(ii)
$\triangle \mathrm{ACQ}$ and $\triangle \mathrm{AQP}$ are on the same base $AQ$ and between the parallels $\mathrm{AQ}$ and $\mathrm{CP}$.
Therefore,
$ar(\triangle ACQ)=ar(\triangle AQP)$
Subtracting $ar(\triangle ABQ)$ on both sides, we get,
$ar(\triangle ACQ)-ar(\triangle ABQ)=ar(\triangle AQP)-ar(\triangle ABQ)$
$ar(\triangle \mathrm{ABC})=ar(\triangle \mathrm{BPQ})$
$\frac{1}{2} \operatorname{ar}(\mathrm{ABCD})=\frac{1}{2} \operatorname{ar}(\mathrm{PBQR})$
From (i) and (ii),
$\operatorname{ar}(\mathrm{ABCD})=\operatorname{ar}(\mathrm{PBQR})$
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