Use cylindrical shells to find the volume of the cone generated when the triangle with vertices (0, 0), (0, r), (h, 0), where r > 0 and h > 0, is revolved about the x-axis.
a) ( /{1}/{3} π r² h )
b) ( /{1}/{2} π r² h )
c) ( /{2}/{3} π r² h )
d) ( π r² h )