What is the relationship between the radius and diameter of a circle?

The relationship between the radius and diameter of a circle is defined such that the diameter is always twice the length of the radius. The radius is the distance from the center of the circle to any point on its boundary, while the diameter is the distance across the circle through the center, connecting two points on the boundary. Mathematically, this relationship can be expressed as Diameter = 2 * Radius.

In this context, since the diameter encompasses two radii (one on each side of the center), it is clear that the diameter will always be twice as long as the radius. This fundamental aspect of circles is essential in understanding various properties and calculations related to circles, such as their circumference and area.

The other options do not accurately represent the relationship; for instance, dividing the radius by 2 or adding 1 does not convey the correct proportional relationship between the two. Similarly, suggesting that the diameter is three times the radius also misrepresents the geometric properties of a circle. Thus, option A is the accurate statement reflecting this essential relationship in circle geometry.