See how the curved surface of the cone can be flattened to a sector, which then be dissected and rearranged to see that its area is π r l, where r and l are the base radius and the slant height of the cone respectively.
This applet combines the previous 3D applet ([url]206987[/url] or [url]166737[/url]) and its 2D counterpart ([url]161406[/url]) in a single applet.
Anthony C.M. Or
GeoGebra Institute of Hong Kong
