S: My radius circumference diameter book
1: Radius is the distance from the center to the boundary.
2: Diameter is the line segment from one boundary of a circle to the other boundary.
3: Circumference is the distance around the circle.
4: Relationships Radius x2 is diameter diameter \2 is radius Diameter x3 is Circumference Circumference \3 is Diameter Radius x6 is Circumference Circumference \6 is Radius
5: This is a pi sign it is equal to 3.