The idea here is that we want to take very thin "slices" perpendicular to the axis we are rotating around. These slices will function as radii that we plug into the area function of the circle, A = Tr². We then can get volumes by multiplying by little changes (dx or dy). Finally, we sum over these volumes (which are very thin!) to get the volume of the entire cone. So, we need to slice from y = 0 to y = x, meaning the radius at each point is given by 0 to x = h to get the integral x – 0 = x. We then integrate from x = ch So Area(circular slices) dæ which would be T(x)² dx. I will leave it to you to evaluate this integral to get the desired result.