If I have a cone and divide it into infinately small slices. Wouldn't both sides of one slice have the same area and wouldn't the next slice (and so on) have the same area as the slice before. So wouldn't your cone actually be a cylinder? My answer is no, because the reasoning is wrong. If I had infinately small slices I would never complete the cone/cylinder in the first place. And the assumption of both sides having the same area is an assumption to be able to integrate, but is not reality. If we're talking about the perfect cone then both sides of the slices should have different areas even if the slices were infinately small. What's your view on this?