NCERT Solutions
Class 9 Maths
Areas of Parallelograms and Triangles

Ex.9.4 Q.4
In Fig. 9.32, ABCD is a parallelogram and BC is produced to a point Q such that AD = CQ. If AQ intersect DC at P, show that ar (BPC) = ar (DPQ).
[Hint: Join AC.]
It is given that ABCD is a parallelogram.
AD || BC and AB || DC
[Opposite sides of a parallelogram are parallel to each other]
Join point A to point C.
Consider ∆APC and ∆BPC,
∆APC and ∆BPC are lying on the same base PC and between the same parallels PC and AB.
Therefore,
Area (∆APC) = Area (∆BPC) ..........(1)
In quadrilateral ACDQ, it is given that
AD = CQ
Since ABCD is a parallelogram,
AD || BC (Opposite sides of a parallelogram are parallel)
CQ is a line segment which is obtained when line segment BC is produced.
So, AD || CQ
We have,
AC = DQ and AC || DQ
Hence, ACQD is a parallelogram.
Consider ∆DCQ and ∆ACQ
These are on the same base CQ and between the same parallels CQ and AD.
Therefore,
Area (∆DCQ) = Area (∆ACQ)
=> Area (∆DCQ) − Area (∆PQC) = Area (∆ACQ) − Area (∆PQC)
=> Area (∆DPQ) = Area (∆APC) ... (2)
From equations (1) and (2), we obtain
Area (∆BPC) = Area (∆DPQ)