Question

sign convention for concave and convex lens

Answer 1

the objects or distances on the left of lenses are all negative while on right are all positive..
the heights or distances taken upward are positive while taken downward are negative....

Answer 2

1.All distances on the principal axis are measured from the optical center.
2.The distances measured in the direction of incident rays are positive and all the distances measured in the direction opposite to that of the incident rays are negative.
3.All distances measured above the principal axis are positive. Thus, height of an object and that of an erect image are positive and all distances measured below the principal axis are negative.

hope it helps u...