posted by Dave .
the point (3,-4,5), (1,0,5), and (3,1,-2) are three out of four vertices of a parallelogram ABCD. Explain why there are three possibilities for the location of the fourth vortex, and find the point?
the three vertices determine a plane. The 4th point must lie in that plane, but you can pick any of the three points to be the "origin" relative to the other two.