The diagram shows the point , along with several points that are 5 units away from . For some points, it is easy to see their distance from . For example, we can count or subtract to see that , , and are all 5 units away from .

For other points, we need to calculate the distance. Let's look at the point . To calculate the distance from to , we can let stand for the distance, and set up the Pythagorean Theorem: Evaluate the left-hand side to find that . Now is the positive number that squares to make 25, which means that  really is 5 units away from . 

The point also looks like it could be 5 units away from . To find its distance from , we can do a similar calculation: . Evaluating the left side, we get . This means that must be a little more than 5. So  is not exactly 5 units away from .