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(A) For a concave lens,the magnification $m$ is given by the formula $m = \frac{f}{f+u}$,where $f$ is the focal length (taken as negative for a concav

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$(x-1)f$

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(A) For a concave lens,the magnification $m$ is given by the formula $m = \frac{f}{f+u}$,where $f$ is the focal length (taken as negative for a concave lens) and $u$ is the object distance (also negative).Given that the image size is $(1/x)$ of the object size,the magnification $m = +\frac{1}{x}$ (since the image formed by a concave lens is virtual and erect).Substituting $f = -f$ and $m = \frac{1}{x}$ into the lens formula $m = \frac{f}{f+u}$:$\frac{1}{x} = \frac{-f}{-f+u}$$-f + u = -xf$$u = f - xf$$u = -f(x-1)$Taking the magnitude of the distance,the distance of the object from the lens is $(x-1)f$.

$A$ concave lens of focal length $f$ produces an image $(1/x)$ of the size of the object. The distance of the object from the lens is:

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