How to Master Unique Rectangle Type 2 in Sudoku

Building on the primary logic of avoiding unresolvable grids, the Unique Rectangle Type 2 technique handles situations where an extra candidate leaks into two corners of a rectangle instead of just one. By leveraging the uniqueness principle of Sudoku, you can turn this potential trap into a powerful elimination tool.

Identifying Unique Rectangle Type 2

Look for four cells forming a rectangle across two 3×3 blocks, two rows, and two columns:

In this case, we have two pure bi-value cells and two three-value cells sharing the same extra candidate, 2. So we are looking at Unique Rectangle Type 2.

Take a look at this example:

• Two Pure Corner Cells: Contain strictly the base pair (6 and 9),
• Two Modified Corner Cells: Both contain the base pair plus the same single extra candidate (2),

The Logic Behind the Elimination

Because two corners contain the extra digit 2, we know that one of these three-value cells must contain 2.

Otherwise, if none of these cells contain 2, we get a “deadly pattern,” because the puzzle would have more than one valid solution for this grid configuration. In that case, each of the highlighted cells could take the values 6 and 9 in two different ways.

Since the puzzle is guaranteed to have only one valid solution, the digit 2 is mathematically forced into one of those two corners.

The Elimination Rule

Because the digit 2 is locked into these two specific cells, it acts as a strong pair along their shared unit.

So we can safely eliminate 2 from any cell that can see both of these cells at the same time.

📍 Where Exactly to Erase Candidates?

1. Locate the two corners containing the extra digit 2.
2. Find any empty cell outside the rectangle that shares a row, column, or 3×3 block with both of these corners simultaneously.
3. Erase the number 2 from the pencil notes of those intersecting cells.

Keep Your Momentum Going

Unique Rectangle Type 2 proves that even when extra candidates spread across multiple cells, the grid’s underlying balance remains strictly predictable. Spotting these twin extra candidates allows you to clear surrounding clutter without building complex, multi-digit chains.

Ready to dismantle the deadly pattern? Put your expert scanning to the test right now on our Expert Sudoku Puzzles, keep your pencil notes active, and hunt for those matching extra candidates!