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

"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.

Angle onp = 43°angle lno = 137°angle mnp = 137°