The resolution of a telescope is ultimately limited by the diameter of its objective lens or mirror. An amateur astronomer's telescope has a 5.2 in. diameter mirror. (Take lambda to be 550 nm, near the center of the visible spectrum.)
(a) What is the minimum angular separation (in arc seconds) of two stars that can be resolved with the 5.2 in. scope?
(b) What is the minimum distance (in km) between two points on the Moon's surface that can be resolved by the 5.2 in. scope? (Note: The average distance from Earth to the Moon is 384,400 km.)
You should have formula for diffraction-limited resolution in your textbooks, however, just in case, here is a web page on the subject:
Equation (17) on this page gives the commonly accepted ...
Solution explains how the answers are arrived at, and shows the relevant computations.