Given :
The vertices of parallelogram ABCD are A(4,0,3), B(3,4,-2),C(-2,0,1).
To Find :
The coordinates of fourth vertices.
Solution :
We know, the vertices are ABCD .
Let, point D is (x,y,z) .
Also, diagonals of a parallelogram bisect each other.
Let, point of intersection of daigonal is O.
Coordinates of O are :

O(1,0,2)
Value of point O through BD.

Therefore, the fourth vertices is D( -1,-4,6 ).