A concave mirror is a part of hollow sphere of radius 40 cm. What will be the focal length of concave mirror?

Explanation

To find the focal length of a concave mirror given its radius of curvature, we can use the relationship between the focal length (f) and the radius of curvature (R). The formula is:

\[ f = \frac{R}{2} \]

### Step-by-Step Solution:

1. **Identify the Radius of Curvature (R)**:
- The problem states that the radius of the hollow sphere (which is the radius of curvature of the concave mirror) is 40 cm.
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