Takin the origin at the vertex, u=-20.0cm ` and`R=5.0cm.
We have, `(mu_(2))/(v)-(mu_(1))/(u)=(mu_(2)-mu_(1))/(R)`
`(1.5)/(v)=(1)/(-20.0cm)+(0.5)/(5.0cm)=(1)/(20cm)`
`rArr v=30 cm`
The image is formed inside the rod at a distance of 30 cm from the vertex.