P is the mid-point of the side CD of a parallelogram ABCD. A line through C parallel to PA intersects AB at Q and DA produced at R. Then:
Given in a parallelogram ABCD, P is the midpoint of DC.
ABCD is a parallelogram.
∴ BC=AD and BC||AD
Also, DC=AB and DC||AB
Since P is the mid-point of DC.
∴ DP=PC=12DC
Now, QC ∥AP and PC ∥ AQ.
So, APCQ is a parallelogram,
AQ=PC=12DC
=12AB=BQ [∵DC=AB] . . . . . .(i)
Now, in ΔAQR and ΔBQC, AQ = BQ [from Eq. (i)]
∠AQR=∠BQC [vertically opposite angles]
and ∠ARQ=∠BCQ [Alternate interior angles]
∴ ΔAQR=ΔBQC [by AAS congruence rule]
∴ AR = BC [by CPCT rule]
But, BC = DA
∴ AR = DA
Also, CQ = QR [by CPCT rule]