While considering this post, it made me wonder about its generalization in another direction and from the perspective of Galois theory.

**Question:** Is it true that, given four constants ($\alpha,\beta,\gamma,\delta$), then the system,
$$\begin{aligned}
x_1^a+x_2^a+x_3^a+x_4^a &= \alpha\\
x_1^b+x_2^b+x_3^b+x_4^b &= \beta\\
x_1^c+x_2^c+x_3^c+x_4^c &= \gamma\\
x_1^d+x_2^d+x_3^d+x_4^d &= \delta
\end{aligned}\tag1$$
** can be solved in radicals** $x_i$ for any positive integer power ($a,b,c,d$) and $a<b<c<d$?

**Example:** Let's choose the year *Back to the Future* came out,

$$\begin{aligned} x_1+x_2+x_3+x_4 &= \color{brown}1\\ x_1^2+x_2^2+x_3^2+x_4^2 &= \color{brown}9\\ x_1^4+x_2^4+x_3^4+x_4^4 &= \color{brown}8\\ x_1^8+x_2^8+x_3^8+x_4^8 &= \color{brown}5 \end{aligned}$$

Two solutions are given by the roots of the octic,

$$4707 + 9036 x - 7495 x^2 - 5096 x^3 + 3024 x^4 + 1848 x^5 - 896 x^6 - 256 x^7 + 128 x^8 = 0$$

*Magma* says this is $8T47$, has order $1152=2^7\cdot3^2$ and is the largest solvable order for deg $8$. (In fact, it factors over $\sqrt{1441}$). Using the root $r_i$ numbering system of *Mathematica*, we find that,

$$x_1,\, x_2,\, x_3,\, x_4 = r_1,\, r_2,\, r_5,\, r_6\quad \text{(Solution 1)}\\ \text{or}\quad\quad\\ x_1,\, x_2,\, x_3,\, x_4 = r_3,\, r_4,\, r_7,\, r_8\quad \text{(Solution 2)}$$

**Remarks:** Using generic ($\alpha,\beta,\gamma,\delta$)

- For exponents $a,b,c,d = 1,2,c,8$ and $c=3,4,5$, one ends up with a $8T47$ octic with order $1152=2^7\cdot3^2$.
- For $a,b,c,d = 1,2,6,7$, one gets a $12T294$ with order $82944 = 2^{10} \cdot 3^4$.
- For $a,b,c,d = 1,2,c,8$ and $c=6,7$, one now gets a $16T1947$ with order $7962624 = 2^{15}\cdot3^5$. These three are the
solvable orders for their respective degrees.*largest* - Using others yields deg $20,24,$ etc.

So, is the system $(1)$ always solvable in radicals?