Question: An infinitesimal patch views a circular area source of constant exitance frontally along the axis of symmetry of the source. Compute the radiosity of the patch, due to the source exitance E(u) as a function of the area of the source and the distance between the center of the source and the patch. You may have to look the integral up in tables - if you don't, you're entitled to feel pleased with yourself - but this is one of few cases that can be done in closed form. It will be easier to look up if you transform it to get rid of the cosine terms.