Sudoku X · Hard

Hidden Pair in Sudoku X

Two digits that fit in only two cells of a house. Every other candidate in those cells is eliminated.

The idea

When two digits can go only in the same two cells of a house, those cells must hold them. Their other candidates can go.

The diagonals are houses in Sudoku X, so a hidden pair can hide on one.

Worked examples

2 positions from real Sudoku X puzzles on this site, the familiar case first. Step through each one: the board lights what each step talks about, and the arrows show what rules what out.

Two digits, two cells, in a box

Hard puzzle · Hidden Pair

In box 8, look for two digits that fit in only two cells.

Step 1 of 4Step 2 of 4Step 3 of 4Step 4 of 4

Two digits, two cells, on a diagonal

Hard puzzle · Hidden Pair

Look along the lit diagonal for two digits with only two places.

Step 1 of 5Step 2 of 5Step 3 of 5Step 4 of 5Step 5 of 5

Where it fits

HardHidden Pair is a Hard technique: Hard Sudoku X puzzles are the first to need it.

The Classic Hidden Pair lesson teaches it on a plain 9×9 board. The Sudoku X overview explains the rule and the levels.

Hidden Pair in the other styles: Jigsaw, Thermo, Windoku, Arrow, Kropki.

Try it on a Hard Sudoku X puzzle. Next Step points it out when it is the move.

The worked examples, every step

Two digits, two cells, in a box

Hard Sudoku X puzzle · Hidden Pair

  1. In box 8, look for two digits that fit in only two cells.
  2. In box 8, {4, 7} can only go in R9C4, R9C6. Those cells must hold those digits, so their other candidates can go.
  3. Keep only {4, 7} in R9C4, R9C6.
  4. Done: 1, 2 and 3 are eliminated from R9C4; 3 and 8 are eliminated from R9C6.

Two digits, two cells, on a diagonal

Hard Sudoku X puzzle · Hidden Pair

  1. Look along the lit diagonal for two digits with only two places.
  2. On the anti-diagonal (from R1C9 to R9C1), look for two digits that fit in only two cells.
  3. On the anti-diagonal, {2, 9} can only go in R1C9, R9C1. Those cells must hold those digits, so their other candidates can go.
  4. Keep only {2, 9} in R1C9, R9C1.
  5. Done: 3 is eliminated from R1C9; 3 and 8 are eliminated from R9C1.

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