Lines in Fields of Three

Geometry Level 3

How many unique lines are there in F 3 2 \mathbb{F}^2_3 that pass through the point ( 0 , 0 ) (0,0) ?


The answer is 4.

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1 solution

Suppose the elements of F 3 \mathbb{F}_3 are of the form 1 -1 , 0 0 and 1 1 , so that elements of F 3 2 \mathbb{F}_3^2 are pairs of the three elements defined previously. One can represent this space geometrically as a 3 × 3 3 \times 3 grid, with the origin being the middle square in this grid. It should be clear then that there should be four lines going through this origin, with direction vectors ( 1 , 0 ) \left(1,0\right) , ( 1 , 1 ) \left(1,1\right) , ( 1 , 1 ) \left(-1,1\right) and ( 0 , 1 ) \left(0,1\right) .

P.S. An alternative representation of this problem is to consider how many possible winning combinations there are in Tic-Tac-Toe that involves the middle square.

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