"interverted" or "inverted?"
The vertical height of an inverted cone with base diameter 6 cm and slant height of 6 cm can be found using the Pyth. Thm. Draw or imagine a triangle whose height is h and whose base is 3 cm (not 6) and whose hypotenuse is 6 cm.
Then h^2 + (3 cm)^2 = (6 cm)^2, or h^2 + 9 cm^2 = 36 cm^2, or h^2 = 27 cm^2.
Then the height of the triangle, as well as of the cone, is h = +√27, or
h = +3√3.