Question

relation between focal length object distance image distance of concave mirror

Answer 1

The position of the image is obtained by drawing a ray diagram.

Consider the D A1CB1 and D ACB

[when two angles of D A1CB1 and D ACB are equal then the third angle 

But ED = AB

From equations (1) and (2)

If D is very close to P then EF = PF

But PC = R, PB = u, PB1 = v, PF = f

By sign convention

PC = -R, PB = -u, PF = -f and PB1 = -v

 Equation (3) can be written as

Dividing equation (4) throughout by uvf we get

Answer 2

image distance is the distance of image from pole. it is denoted by v
object distance is dist. of object from pole.it is denoted by u.
Focal length(f) is 1/v + 1/u
Hope this will help u