X-Wing in Sudoku: Explained on a Live Grid
The X-wing looks at two rows at once. It works on one digit at a time, so this lesson starts with only that digit pencilled in. Cells are named by row and column: r5c2 is row 5, column 2.
Step 1 of 4
Four corners
Only the 9s are pencilled in here. In row 5 the 9 fits only r5c2 or r5c7. In row 7 it fits only r7c2 or r7c7: the same two columns. Those four cells are ringed.
Either the 9s go in r5c2 and r7c7, or in r5c7 and r7c2. Both ways, column 2's 9 and column 7's 9 are in rows 5 and 7. That's an X-wing: every other cell of columns 2 and 7 loses its 9.
Use the X-wing
Rub out every 9 in columns 2 and 7 outside rows 5 and 7. Then look for a row, column or box where the 9 has one place left.
Your move
Clear the 9 from columns 2 and 7 outside rows 5 and 7, then place the 9 that is forced.
Which 9s go?
The X-wing sits in rows 5 and 7, columns 2 and 7. Which cells lose their 9?
Find the X-wing
Every candidate is pencilled in this time, and no cell has just one. Look for a digit with exactly two places in each of two rows, in the same two columns. More than one such pattern is here, but only one clears a candidate.
Your move
Find the X-wing that unlocks a digit, then place it.
What you learned
- An X-wing is one digit with exactly two places in each of two rows, in the same two columns.
- Those two columns get their digit in those two rows: clear it from the rest of both columns.
- It works the other way round too: two columns, the same two rows, and the rows lose the digit.
In this course
Unit 1The rules
Unit 2Solving techniques
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