1. The problem statement, all variables and given/known data Show that the volume of a sphere of radius r is V = (4/3)πr^2 2. Relevant equations calculus, integration 3. The attempt at a solution I have the solution in the book but it's confusing me, I'll attach a picture. So I get lost where it starts talking about a cross-sectional area all of a sudden multiplying by ∏. What's going on here?!