The directions of the centroid are just the normal of the directions of the vertices. So to track down the x facilitate of the orthocenter, include the three vertex x organizes and gap by three. Rehash for the y organize.
Assume the coordinates of the third vertex C be (x, y)
Given in the question, $A(3,2)$ and $B(-2,1)$ are two vertices of a triangle ABC
Then, we know that the coordinates of centroid of the triangle are
$\left( \frac{x+3-2}{3},\frac{y+2+1}{3} \right)$
Given in the question that the centroid for the triangle is $(5/3,-1/3)$.
$\frac{x+3-2}{3}=5/3$and $\frac{y+2+1}{3}=-1/3$
$⇒x+1=5⇒y+3=-1$
$⇒x= 4⇒y=-4$
Therefore, the coordinates of the third vertex C is $(4,-4)$