---
title: "Unique Rectangle: Sudoku Technique #29 | Sudoku Flow"
description: "Unique Rectangle, explained step by step in a short video lesson. The puzzle has a single solution, so a pattern that would allow two solutions must be avoided."
url: https://sudokuflow.com/lessons/uniqueRectangle/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / Unique Rectangle

Lesson 29

# Unique Rectangle

## The rule

The puzzle has a single solution, so a pattern that would allow two solutions must be avoided.

## Step by step

1. These four cells form a rectangle in exactly two boxes, and each contains the candidates 3 and 7. If all four were limited to only those two candidates, they would form a deadly pattern.
2. To avoid two solutions, the candidates 3 and 7 can be removed from the cell with extra candidates.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/unique-rectangle.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where Unique Rectangle applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

Unique Rectangle practice board:

```text
8* 3  7  | 9  1  4* | 5* 6* 2*
9  1* 4  | .  .  .  | 8  3* 7
.  .  2* | 8* 3  7* | 9* .  .
---------+----------+---------
3  7* 8  | .  9  .  | .  2  .
1* 2  .  | 4  7* 3* | 6  8* .
4* .  6* | .  .  .  | 3* 7  .
---------+----------+---------
7* .  .  | 3* 4  .  | 2  .  6*
.  .  3  | 7  2  .  | .  9  8
2* .  1  | .  .  .  | 7* .  3
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.