What is lens formula ? Give its sign conventions and assumptions.

Explanation

### Step-by-Step Solution:

1. **Understanding the Lens Formula**:
- The lens formula relates the focal length (F), the object distance (U), and the image distance (V) of a lens. It is expressed as:
\[ \frac{1}{F} = \frac{1}{V} - \frac{1}{U} \]
- Here, F is the focal length of the lens, V is the distance from the lens to the image, and U is the distance from the lens to the object.
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