Question

sign conventions for object distance, image distance and focal length of a diverging lens​

Answer 1

As such as sing convention for mirror

Answer 2

Explanation:

SIGN CONVENTION - DEFINITION

Sign convention is a set of rules to set signs for image distance, object distance, focal length, etc for mathematical analysis of image formation. According to it:

Object is always placed to the left of lens.

All distances are measured from the optical center of the mirror.

Distances measured in the direction of the incident ray are positive and the distances measured in the direction opposite to that of the incident rays are negative.

Distances measured along y-axis above the principal axis are positive and that measured along y-axis below the principal axis are negative.

Note: Sign convention can be reversed and will still give the correct results.  

        Convex lens has positive focal length and concave lens has negative focal length.