Radius is half times the diameter. When the surface area or the volume is known, the radius of a circle or a sphere can be calculated.
Radius of a circle
This is the formula to calculate the radius of a circle, with A being the surface area of the circle:
Radius of a sphere
This is the formula to calculate the radius of a sphere, with A being the surface area of the sphere and V being the volume of the sphere:
- The surface area of a circle is 23. What is the radius?
- How large is the area of a circle with diameter 2?
- What is the volume of a sphere with radius 8?
- A sphere has a volume of 15. How large is the area?
- The volume of a sphere is 45. What should the radius of a circle be, if the surface areas are equal?