Making a cone
This applet shows folding of a paper cone. Various geometric features in this process can be discussed.
In particular, the relation among the angle of the sector (), slant height (l) and base radius of the cone (r) can be carefully examined:
Drag V to fold/unfold the cone. Drag B to change the size of the paper sector.
Check this tutorial for this construction:
https://ggbm.at/mrXDrjMQ