Question

Two lenses having focal length f1 and f2are placed coaxially at a distance x from each other what is the focal length of the combination

Answer 1

1/f=1/f1+1/f2. This is u r answer.

Answer 2

Answer: The inverse of combination of focal lengths are the addition of inverse of focal length of first lens to the inverse of second lens

                        1/F=1/f1+1/f2