Question

what distance we take for real image of lens​

Answer 1

Answer:

If the lens equation yields a negative image distance, then the image is a virtual image on the same side of the lens as the object. If it yields a negative focal length, then the lens is a diverging lens rather than the converging lens in the illustration.

Explanation:

Images, real and virtual. Real images are those where light actually converges, whereas virtual images are locations from where light appears to have converged. Real images occur when objects are placed outside the focal length of a converging lens or outside the focal length of a converging mirror.