# How do I solve this sudoku without guessing

I am fairly new to Sudoku and couldn't find how to progress with this one without guessing.

• Did you try this solver?
– JLee
Commented Sep 27, 2022 at 14:05

Not sure if this counts as guessing, but R4C2 can be solved:

Look at R5C1.
If it's a 5, then R4C2 is a 1.
If it's a 6, then R8C1 is a 7, R7C2 is a 5 and R4C2 is a 1.

• What number would be R6C1 ? Commented Sep 28, 2022 at 14:24
• @IISkullsII It will come out to be a $4$, once you begin simplification from R4C2 (I'm assuming that you're asking what the final value would be, and not some way to get it before you get R4C2). Commented Sep 28, 2022 at 16:16
• More or less. I wasnt precise enough. Assuming, the OP has entered all possible Values into each Cell. I'm still not convinced, that if R5C1 is either 5 or 6, that R4C2 must be 1. If i assume R5C1 is 6, then R5C2 has to be 2, which results in R6C3 to be 4 and R6C1 has to be 1, which would render R4C2 into nothing else than 5. Commented Sep 29, 2022 at 6:11
• @IISkullsII That's actually really good deduction, and you're absolutely right so far. However, you're actually on your way to showing that R5C1 is not a $6$, which you can probably post as an answer, it's a very good observation. Indeed, once you assume that R5C1 is a $6$, the you've correctly shown in your comment that R4C2 is a $5$, but then R7C2 is a $7$ and then R8C1 must be a $6$. That leads to two $6$s in the same column (R5C1 and R8C1), hence giving a contradiction. Therefore, you've actually shown that R5C1 must be a $5$. Commented Sep 29, 2022 at 12:09

For those that may have seen a manual or website on Sudoku solving, it is worth trying to spot a Y-Wing on this board. This is instructive because guessing in general is an art, while attempting to spot X and Y wings(for example) is something that solvers can be trained specifically to look out for.

The other answer is sound as well: given that the bottom right corner has many cells with only two candidates, forcing chains are a natural strategy.

Here's the Y-Wing:

[56] on R5C1, [67] on R8C1 and [57] on R7C2 form a Y-Wing, which shows that 5 cannot be a candidate for R4C2. Thus, R4C2 = 1.

Note that after one uses the Y-Wing to resolve a cell, the rest of the puzzle can easily be solved without any more complicated techniques.