Assume we have a cone, as shown on the left of the diagram, with its vertex at A and base a circle BC(C’)B passing through points B and C.
If we cut it around the line AC, expand it out , it’s a circular sector ACBC’A, where the original base circle BC(C’)B now is an arc CBC’, as shown on the right side .
If we cut the cone, the base BD(D’)B is an ellipse.
Now, if we still cut it along side AD, and expand it out. What is the shape of the curve DBD’ ?
