Let n be a positive integer greater than or equal to 3. Let a,b be integers such that ab is invertible modulo n and \((ab)^{-1}\equiv 2\pmod n\). Given a+b is invertible, what is the remainder when \( (a+b)^{-1}(a^{-1}+b^{-1})\) is divided by n?
I don't understand! An explanation would really help, I don't know where to start even.
