Hidden Pairs
The Hidden Pairs technique is the inverse of Naked Pairs. It can be harder to spot because the pair is "hidden" among other candidate numbers in the cells.
How it Works
You are looking for a situation where two candidate numbers appear in exactly two cells within a specific group (row, column, or block), and nowhere else in that group. Even if those two cells have other pencil marks in them, the fact that our two target numbers can ONLY go in those two cells means they must be the answer.
Therefore, you can safely delete all the "extra" candidate numbers from those two cells, effectively turning the Hidden Pair into a Naked Pair.
How to spot and apply Hidden Pairs in Sudoku
- Find the pairLocate two candidate numbers that only appear in exactly two cells within a row, column, or block.
- Eliminate noiseBecause those two numbers must go in those two cells, you can safely remove all other candidate numbers from those two cells.