Let V be a finite set of points in three-dimensional space. Let S1,S2,S3 be the sets consisting of the orthogonal projections of the points of V onto the yz-plane, zx-plane, xy-plane, respectively. Prove that ∣V∣2≤∣S1∣⋅∣S2∣⋅∣S3∣, where ∣A∣ denotes the number of elements in the finite set A. inequalitiesgeometry unsolvedgeometry