A circle is a basic shape in math.

It is made up of all the points on a flat surface that are the same distance from a center point.

This distance is called the radius, and it’s important because it affects how big the circle is.

Parts of a Circle:

1. Radius ($r$):

   • The radius is the space from the center of the circle to any point on its edge.
   • For example, if the center of a circle is point $O$, and point $A$ is on the edge, then the distance from $O$ to $A$ is the radius.

2. Diameter ($d$):

   • The diameter is twice the length of the radius.
   • It goes from one edge of the circle to the other, passing through the center.
   • We can write this as: $d = 2r$
   • So, if the radius is 5 units, the diameter would be 10 units.

In short, the radius and diameter help us understand how big a circle is.

If you know one of them, you can easily find the other.

This is really helpful when using formulas to find the area and the distance around the circle:

• Area: $A = \pi r^2$
• Circumference: $C = \pi d$