Question

How are the units of measurement called “radians” related to the radius of a circle?

Answer 1

A radian is a unit of measurement that measures the central angle of a circle. A central angle measuring one radian intercepts or forms an arc whose length is equal to the radius of the circle.

Explanation:

Answer 2

"Radians" are unit of angular measure used in mathematics. It is a measure based on the "Radius" of the circle (Radius is the straight line from the center of the circle to the circumference of a circle).
Radian is the angle made when we take the radius and wrap it around the circle. (It is the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc.)
The radian is represented by the symbol rad.