Slant Height of a Cone
The slant height is the distance from any point on the circumference to the apex of the cone.
By applying the Pythagorean theorem, the slant height of the cone is equal to:
Slant Height of a Truncated Cone
The slant height is the shortest possible distance between the edges of the two bases.
The slant height of the truncated cone is obtained by applying the Pythagorean theorem for the shaded triangle: