Question

what is the lens formula

Answer 1

1/f = 1/v - 1/u...
It is the lens formula

Answer 2

$\huge\bold \red{Heya\:User!}$

$\huge \underline {Answer \:will \:be-}$

$<b >$Lens formula can be defined as the formula which provides a relationship between the distance of image (v), distance of the object (u) and the focal length (f) of the lens. It is written as -

1/f = 1/v − 1/u

where, v is the distance of image from the optical centre of the lens
u is the distance of object from the optical centre of the lens
f is the focal length of the lens

This formula is applicable for both kinds of lens (concave lens and convex lens)

Regards
@Alan ✌