# A concave mirror produces a real image n times the object. Find u in terms of f and n.

Given, V =nU

Mirror formula, $\frac{1}{v}+\frac{1}{u} = \frac{1}{f}$

In concave mirror

$\frac{1}{-nu}+\frac{1}{-u} = \frac{1}{-f}$

$\frac{1}{n} +1 = \frac{u}{f}$

$\Rightarrow u = f\left ( \frac{n+1}{n} \right )$

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