sil...@math25.mathematik.uni-bielefeld.de (Torsten Sillke) writes: >On the 2*2*2 grid you can take 5 points, such that no 4 points lay on a >plane. The only possibility (up to symmetry) is: > o . . o > o o o . >Can you find the only possibility to take 8 points in the 3*3*3 grid >with the same property?
How about
. o . o . . . . o . . o . . . o . . o . . . . o . o .
In article <1992Nov27.161606.1...@odin.diku.dk>, torb...@diku.dk (Torben AEgidius Mogensen) writes:
> sil...@math25.mathematik.uni-bielefeld.de (Torsten Sillke) writes: >> On the 2*2*2 grid you can take 5 points, such that no 4 points lay >> on a plane. [...] Can you find the only possibility to take 8 >> points in the 3*3*3 grid with the same property? > How about > . x . x . . . . o > . . x . . . x . . > o . . . . x . x .
Sorry. The six (!) points I marked with x are all in the same plane.
In article <1992Nov27.161606.1...@odin.diku.dk> torb...@diku.dk (Torben
AEgidius Mogensen) writes: >sil...@math25.mathematik.uni-bielefeld.de (Torsten Sillke) writes: >>Can you find the only possibility to take 8 points in the 3*3*3 grid >>with the same property?
>How about
>. o . o . . . . o >. . o . . . o . . >o . . . . o . o .
No, there's a diagonal plane which passes through no less than 6 of these points!
. O . O . . . . o . . O . . . O . . o . . . . O . O .
The six points marked with upper-case "O"s are coplanar.