Final answer:
The diameter of a circle is twice the length of the radius.
Step-by-step explanation:
The relationship between the diameter and the radius of a circle is that the diameter is twice the length of the radius. In other words, the diameter is equal to twice the radius.
For example, if the radius of a circle is 5 units, then the diameter would be 2 times 5, which is 10 units. Similarly, if the radius is 8 units, then the diameter would be 2 times 8, which is 16 units.