In △PQR, let D, E and F be the mid-points of sides PQ, PR and QR respectively.
a. (i) Prove that PQ∥FE and PR∥DF.
b. (ii) Hence, show that quadrilateral PDFE is a parallelogram.
c. (iii) Prove that the area of parallelogram PDFE is equal to one-half the area of △PQR.