Let us assume the hexagon be in I quadrant and one side( containing C) parallel to x-axis ( or i-axis).
OG is vector = OC + CG.
OC is vector = OA + CA.
OA is vector =OB + BA
BA , CA, CG have magnitudes predetermined by sides and angles predetermined by orientation of hexagon.
then use theorum on vector transformations to generalise the result.