If I try to find the surface area of any solid by using cylindrical slices, I'm getting wrong answer. I'm taking this as the formula,
$$S = \int_a^b2\pi y dx$$
where $y$ = height ($2\pi y$ = circumference of the cylinder) $dx$ = width. We can approximate the surface area using cylindrical shells right? If we can approximate volume, we can also approximate surface area right? This is my argument... Please help.