Consider △ RSC and △ PQB
From the figure we know that RC || PB and ∠ CRS and ∠ BPQ and ∠ RSC and ∠ PQB are corresponding angles
It can be written as
∠ CRS = ∠ BPQ and ∠ RSC = ∠ PQB
We know that the opposite sides of parallelogram are equal
SC = QB
By AAS congruence criterion
△ RSC ≅ △ PQB
So we get
Area of △ RSC = Area of △ PQB
Therefore, it is proved that ar (△ RSC) = ar (△ PQB).