Derivation of the equilibrium saturation ratio equation?

[DM1984]

Homework Statement

S=1+(a/r)-(b/r^3)

Homework Equations

need to find r=sqrt(3b/a) and S=1+ sqrt((4a^3)/(27b))) from a derivation of the above formula in #1.

The Attempt at a Solution

0=(3b/r^4) - (a/r^2)

 

[Ray Vickson]

Homework Statement

S=1+(a/r)-(b/r^3)

Homework Equations

need to find r=sqrt(3b/a) and S=1+ sqrt((4a^3)/(27b))) from a derivation of the above formula in #1.

The Attempt at a Solution

0=(3b/r^4) - (a/r^2)

So, what is preventing you from solving this equation?

RGV