function that graph an elipsoid and cone

Hi, i need to create a graphing function thath create a cone and an elipsoid. The inputs need to be a,b and c values that define the canonical equation of a surface .... z/c= (x^2/a^2)+(y^2/b^2), but I do not know how to transform the Cartesian coordinates to cylindrical or spherical according to the figure.

[Star Strider]

You will find the cart2pol and cart2sph functions useful.