TITLE: $\frac{1-a^3}{a}=\frac{1-b^3}{b}=\frac{1-c^3}{c}, a \neq b \neq c$; What is $a^3+b^3+c^3$?
QUESTION [7 upvotes]: $\frac{1-a^3}{a}=\frac{1-b^3}{b}=\frac{1-c^3}{c}\\a \neq b \neq c\\a^3+b^3+c^3=$

Since $\frac{1-a^3}{a}=\frac{1-b^3}{b}$, $a^3=b^2a-\frac{a}{b}-1$.
$\therefore a^3+b^3+c^3=ab^2+bc^2+ca^2-\frac{ab+bc+ca}{abc}-1$
Since $a^3+b^3+c^3=(a+b+c)(a^2+b^2+c^2-ab-bc-ca)+3abc$,
$ab^2+bc^2+ca^2-\frac{ab+bc+ca}{abc}-1=(a+b+c)(a^2+b^2+c^2-ab-bc-ca)+3abc$
(stuck here)

REPLY [2 votes]: It looks like you don't need to do any calculations.

We can construct a new cubic equation with roots $a^3,b^3,c^3.$
$$a^3=x_1,~ b^3=x_2,~ c^3=x_3$$
$$\begin{align}r=\frac{1-a^3}{a}=\frac{1-b^3}{
b}=\frac{1-c^3}{c}\end{align}$$
$$\begin{align}&\implies1-a^3=ar \\
&\implies(1-a^3)^3=a^3r^3 \\
&\implies(1-x)^3=xr^3 \\
&\implies1-3x+3x^2-x^3-xr^3=0 \\
&\implies x^3-3x^2+x(r^3+3)-1=0 \\
&\implies x_1+x_2+x_3=3 \\
&\implies a^3+b^3+c^3=3.\end{align}$$