Question

A concave mirror forms a real image at 17.0 cm from the mirror surface along the principal axis. If the corresponding object is at ta distance of 36.0 cm, what isi the mirror's focal length?

let u be the object distance
let v be the image distance

v=17 cm
u=36 cm

1/f = 1/u + 1/v
= u+v
___
uv

so f=uv
____
u+v

= 17*36
_____
17+36

= 11.55cm

is this done correctly?
drwls
Yes