In a circle, there are two important parts: the radius and the diameter.

• Radius: This is the distance from the center of the circle to any point on the edge. We call it $r$.

• Diameter: This is the distance across the circle, passing through the center. It connects two points on the edge. We call it $d$.

Here’s a simple way to remember the difference:

The diameter is always twice as long as the radius. You can see this in the equation:

$$d = 2r$$

So, if you know the radius, you can find the diameter by just multiplying it by 2.

Easy, right?