How to prove this density result?

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

• I'd like to know the formula to find the density of any planet, inside our solar system. It is for a math project at my school in which I need to use integrals. I'm taking this initiative from a Nasa exercise called "The Internal Density and Mass of the Sun", in which they give me the density as D(x)= 519x^4 - 1630x^3 +1844x^2 - 889x + 155 and then they say that the radius goes from x=0 from the core, to x=1 on the surface. Which would give me an integral with values to replace later 1,0. Then, the result of that I multiply it by (6.9x10^10)^3 to get the total astronomical value of Mass in grams. The link to the file is: http://spacemath.gsfc.nasa.gov/weekly/6Page102.pdf

• Answer:

  Why wouldn't you just divide the mass of the planet by its volume? Why do you need an integral? Is the mass, or volume subject to change??? Volume of a sphere: (4πr^3)/3