## Fundamentals of Physics Extended (10th Edition)

$R=36cm$
To find the radius of curvature, use the equation $$R=2f$$ "The distance between the focal point and the mirror" is defined as the focal length. Therefore, the focal length is $18cm$. Since the mirror is concave, the value of the focal length is positive. Substituting this value into the equation yields $$R=2(18cm)=36cm$$