1. The problem statement, all variables and given/known data A combination of two thin convex lenses of equal focal lengths,is kept separated along the optic axes by a distance of 20 cm between them.The combination behaves as a lens system of infinite focal length.If an object is kept at 10 cm from the first lens,its image will be formed on the other side at a distance x from the second lens.Find x. 2. Relevant equations 1/f=1/v + 1/u where f is focal length,u is object distance and v is image distance. 3. The attempt at a solution Can the above equation be applied for the lens system as a whole,instead of just a single lens at a time? If it can be applied,then I think the problem can be solved in the following way: Since f of the lens system is infinity,this means that rays initially travelling parallel to the axis before the 1st lens,will continue to do so after passing through 2nd lens.The lens system behaves symmetrically.If we apply the above equation to the system as a whole,we get v= -10 cm and the image is virtual.Therefore x= 1o cm.Is this answer and reasoning correct?