What is the formula for density (D x), Mars or Jupiter?

I want to know the formula for determining the density of a planet Within our solar system. It is for a math project for my school I have to use the integrals. Take this initiative to pursue the NASA called "density and the inner mass of the Sun "where I give the density of D (x) = 519x ^ 4 – 1630x ^ 3 1844 x ^ 2 – 889x + 155, then say that the radius increases from x = 0 of the base x = 1 on the surface. Who would give me a full replacement value with the latest 1.0. Then the result is multiplied by (6.9×10 ^ 10) ^ 3 for the value total mass in grams astronomical. The link to file: http://spacemath.gsfc.nasa.gov/weekly/ 6Page102.pdf

Why not divide the mass of the planet by its volume? Why do you need a complete? Is the mass or volume under Subject to change?? Volume of a sphere (4πr ^ 3) / 3

Planet X – The Truth

CPR Car Planet Racing Mazda RX7 – 450hp – T70 Turbo – Andy Clark