Is it possible to choose distinct points in the space such that no three of them lie on the same line, and choose distinct planes in a way that each plane passes through at least of the chosen points and each triple of points belongs to one of the chosen planes?
Solution
Solution:
No. Suppose such a choice exists. Let be the number of points on the planes respectively. Note that for . It is clear that
We first show for all . Indeed, if at least one is greater than , then
which is impossible.
Now suppose among all the 's, of them are equal to and of them are equal to . Then we have and
This gives , which is again impossible. Therefore, such a choice does not exist.
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