- Code: Select all
*--------------------------------------------------------------*
| 28 7 4 | 3 9 15 | 15 6 28 |
| 6 1 *5-28 | 248 a28 7 | 2458 3 9 |
| 3 9 258 | 1248 6 1258 | 7 148 248 |
|--------------------+--------------------+--------------------|
| 7 3 1 | 6 b28 4 | 28 9 5 |
| 28 6 9 | 5 17 3 | 1248 48 2478 |
| 4 5 d28 | 9 17 c28 | 6 17 3 |
|--------------------+--------------------+--------------------|
| 9 24 7 | 128 3 128 | 48 5 6 |
| 5 8 6 | 7 4 9 | 3 2 1 |
| 1 24 3 | 28 5 6 | 9 478 478 |
*--------------------------------------------------------------*
This where I think you should be in your marked up diagram. Look at the cells I have marked a, b, c, d.
Suppose Cell a is not 2. Then Cell b must be 2, Cell c must not be 2 and Cell d must be 2.
You can reverse this argument and show that if Cell d is not 2 then Cell a must be 2.
So at least 1 of Cell a or d must be 2. You can use exactly the same type of argument to show that at least one of Cell a or d must be 8.
So either (1) Cell a is 2 Cell d is 8 or (2) Cell a is 8 Cell d is 2.
Either way the cell I have marked * can't be 2 or 8 because it is in the same row as Cell a and the same column as Cell d. So Cell * Row 2 Column 3 ( or r2c3 for short ) is 5 !
Also, the reason you can't remove 2 and 8 from Row 2 Column 7 using the Unique Rectangle technique is that there are 4 boxes involved in the rectangle and this technique requires that there are only 2 boxes
involved in the 4 corners of the rectangle. There are only 2 boxes involved in the rectangle of 17's so these have been correctly removed from Row 5 Column 8.
Leren