Six points A,B,C,D,E and F are given. P,Q,R and S
are the centroids of the triangles ABC,ABD,DEF, and CEF
respectively. The centroid of triangle ABC has the position vector
1/3(a+b+c) and
centroid of triangle ABD has the position vector
1/3(a+b+d) given
that position vector of D is d.(Position vectors
of E and F are not given)
Show that P,Q,R,S are the vertices of a parallelogram.