A concave mirror of focal length `f` produces a real image `n` times the size of the object. What is the distance of the object from the mirror?

Explanation

Since image is real, magnification `m` is `-ve`.
Let distance of object from pole is `x`.
`u=-x,m=-n,f=-f`
`m=-(v)/(u)implies-n=(v)/(-x)`
`v=-nx`
`(1)/(v)+(1)/(u)=(1)/(f)`
`(1)/(-nx)+(1)/(-x)=(1)/(-f)implies(1)/(nx)+(1)/(x)=(1)/(f)`
`(1+n)/(nx)=(1)/(f)impliesx=((n+1)f)/(n)`