G(1,1,−2) is the centroid of the triangle ABC and D is the mid point of BC. If A=(−1,1,−4) then D=
12,1,−52
(5,1,2)
(-5,-1,-2)
(2,1,−1)
Centroid G divides the median AD through A internally in the ratio 2:1
⇒G=2D+A3 ⇒D=3G-A2=2,1,-1