a b
, equal to A B.
In the square of its base,
a b c d
, inscribe a circle, which therefore is of the diameter of the base of the cone, A B.
In the square of its top,
e f g h
, inscribe concentrically a circle whose diameter shall equal C D. ([Coroll. Prob. XIII].)
Join the extremities of the circles by the right lines
k l