Two concave spherical mirrors are parts of two spheres of diameters 1:3. What is the ratio of their focal lengths?

Explanation

Here, `(R_(1))/(R_(2)) = (1//2)/(3//2)=1/3`
`f_1=f_2 = (R_(1)//2)/(R_(2)//2) = (R_(1))/(R_(2)) =1/3`.