Q. Find the volume of the solid which is bounded by the cylinders x^2 + y^2 = r^2 and y^2 + z^2 = r^2. To me they don't really look like equations of cylinders, more like circles. Would the term "r" be constant in this case? Or would it be a variable? Even if r is a variable, I don't understand why the equations contain its square, rather than just "r" itself. Are the given equations standard equations for a clinder? I'm just having trouble interpreting the equations at this stage. Help would be apppreciated.