1. The problem statement, all variables and given/known data Two identical moons of mass m maintain opposite positions in the same circular orbit of radius R around a planet of mass M. Find T2 the square of the orbital period. 2. Relevant equations T2=(4*pi2*R3)/ ( G*M ) 3. The attempt at a solution Hi there, well so I tried just inputting that equation for the square of the orbital period as the anwser .And it marked me wrong.my logic behind that was well if one moon orbits with that period.And the two moons are opposite rather each other then they both are going top have the same orbital period.So I guess it would be the right anwser. But as I've said it's not.So I'm puzzled at what's wrong. Did I somehow miss read the question.or am I thinking of a wrong orbital period or something.could someone explain why my anwser is incorrect.And guide me along the right path , so I could improve my understanding of physics. Any help will be greatly appreciated. :) P.S. I don't know if it will work but here's the image I got with the problem.