Is the focal length, image distance and object distance positive or negative for the concave and convex lenses?

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Solution

The object distance is always negative as the object is always placed on the left side of the lens.
Focal length of a convex lens is positive and that of concave lens is negative.
The sign of image distance depends on the position of the object. For concave lens ,image distance is always negative as the image is always formed on the left side of lens. For convex lens the sign depends on the position of object.

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