defining diameter, radius, and circumference 
Definition of the Radius
Radius of a Circle
The radius is defined as the distance from the center point to any point on the edge (circumference) of the circle.
Relationship between Radius and Diameter
The radius is half the length of the diameter.
Formula:
If the diameter ( ext{D}) is known:
Conversely, to find the diameter when the radius is known:
Definition of Circumference
Circumference of a Circle
The circumference is the distance around the circle.
It can also be considered the perimeter of the circle.
Importance of Understanding These Terms
Both radius and circumference are fundamental concepts when studying circles:
They are crucial for calculations involving area, and other properties of circular shapes.