An object is placed in front of a concave mirror of focal length 20 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror?

Explanation

`m= pm 3`
`m=(-v)/u=+3` for virtual image
`v=-3u`
`1/v+1/u=1/f`
`1/(-34)+1/u=-1/20`
`u=-40/3 cm`
`m=(-v)/u=-3` for real image
`v=3u`
`1/v+1/u=1/f`
`1/(3u)+1/u=-1/ 20`
`u=-80 /3 cm`