293. Solve the equation:

$$
x^{4}+2 x^{3}+3 x^{2}+2 x-81600=0
$$

(solved elementarily).
293. $x^{4}+2 x^{3}+2 x^{2}+x^{2}+2 x+1=81601$;

$$
\begin{gathered}
\left(x^{2}+x+1\right)^{2}=81601 \\
x^{2}+x+1-\sqrt{81601}=0 \\
x=-\frac{1}{2} \pm \sqrt{\frac{1}{4}-1+\sqrt{81601}}= \\
=-\frac{1}{2} \pm \sqrt{\sqrt{81601}-\frac{3}{4}}
\end{gathered}
$$