ABCD and AEFD are two parallelograms. Prove that ar (PEA) $=\operatorname{ar}($ QFD $)$
Solution.
Given: Two parallelograms ABCD and AEFD.
To prove: $\operatorname{ar}(\triangle P E A)=\operatorname{ar}(\triangle Q F D)$
Proof:
PQDA is a parallelogram, so $A P\|D Q, P Q\| A D$
Now, parallelograms PQDA and AEFD are on the same base AD and lie between the same parallel lines AD and EQ .
Hence,
$
\begin{aligned}
& \operatorname{ar}(\| g m P Q D A)=\operatorname{ar}(\| g m A E F D) \\
& \operatorname{ar}(P F D A)+\operatorname{ar}(\triangle Q F D)=\operatorname{ar}(\triangle P E A)+\operatorname{ar}(P F D A)
\end{aligned}
$
So, we get:
$
\operatorname{ar}(\triangle Q F D)=\operatorname{ar}(\triangle P E A)
$
Hence proved