A lens of focal length 25.0 cm forms an image 37.5 cm from the lens. What was the object distance?

it can be 15 or 75

Explanation:

using this equation

f = focal length

so = object distance

si = image distance

since we do not now what lens used, I assume from the problem the lens are positive (convex) but I don't know the image position because lens have two side.

1. the positif lens with negative image distance (it means object and image are in the same side of lens)

1/25 = 1/so - 1/37.5

1/so = 1/25 + 1/37.5 = 1/15

so = 15 cm in front of the lens (same side with the image)

2. the positif lens with positive image distance (it means object and image are not in the same side of lens)

1/25 = 1/so + 1/37.5

1/so = 1/25 - 1/37.5 = 1/75

so = 75 cm in front of the lens (not in the same side with the image)

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