In circle geometry, there are three important parts that are all connected: the radius, diameter, and circumference.

• Radius: This is the distance from the center of the circle to the edge. The radius is half of the diameter. If you know the diameter, you can find the radius by using this formula:
  ( r = \frac{d}{2} ).

• Diameter: This is the distance right across the circle, going through the center. The diameter is double the radius. You can find the diameter with this formula:
  ( d = 2r ).

• Circumference: This is the total distance all around the circle. You can calculate it using one of these formulas:
  ( C = 2\pi r )
  or
  ( C = \pi d ).

Isn’t it cool how these parts are all connected?