An object is placed at a distance f in front of a concave lens of focal length f. Locate its image.

Explanation

To solve the problem of locating the image formed by a concave lens when an object is placed at a distance equal to the focal length \( f \), we can follow these steps:

### Step 1: Identify the Given Values
- Focal length of the concave lens, \( f \) (note that for a concave lens, the focal length is considered negative, so \( f = -f \)).
- Object distance, \( u = -f \) (the object is placed at a distance \( f \) in front of the lens).

### Step 2: Write the Lens Formula
The lens formula is given by:
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