1. The problem statement, all variables and given/known data Show that the total energy of the radiation in a volume V at temperature T is Hint: 2. Relevant equations 3. The attempt at a solution The hint doesn't make sense to me, and those are the equation that I found to be perhaps relevant. Do I integrate the second equation? I'm not sure how to start this problem. I think the hint is to help in integrating the second "relevant" equation, so integrating f^3 / exp(hf/K_BT)-1 from zero to infinity should equal pi^4/15?