A "Pares apontadores" strategy applies when a candidate within a 3x3 block appears only two times, and both instances fall on the same row or column. Isso significa the solution for that candidate within this block must be in one of those two cells. Portanto, you can remove that candidate from the notas of all other cells in that row or column outside of the block.
To better understand "Pares apontadores", let's look at an example.
Vamos olhar para the top-left block. All the cells that could possibly contain the number 4 are in a single column. Since the number 4 must appear at least once in this block, one of the highlighted cells must contain the 4.
From this, we can safely eliminate the possibility of 4 being in any of the other cells in this column.
Remember that you can use the same technique for blocks, rows, and columns.
Este é the "Pares apontadores" solving method. Now you can move on to the next Sudoku strategy below, "Triplas apontadoras."