X-Wing Walkthrough

An X-Wing forms when a candidate is restricted to the same two columns in two different rows (or two rows in two columns). The digit must occupy opposite corners of that rectangle, so it can be eliminated elsewhere in those lines.

Sudoku board with pencil-mark candidates before applying the X-Wing technique — Before — candidates pencilled in. There is an X-Wing with the number 5.

There is an X-Wing with the number 5. Applying the X-Wing eliminates 8 candidates and solves 1 cell (struck out in red below; any solved cells shown in green).

The same Sudoku board after the X-Wing technique eliminates 8 candidates and solves 1 cell — After applying the X-Wing.

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