$$x^4-4x^2 = 1$$
Answer
$$ \begin{matrix}x_1 = 2.05817 & x_2 = -2.05817 & x_3 = 0.48587i \\[1 em] x_4 = -0.48587i & \\[1 em] \end{matrix} $$
Explanation
$$ \begin{aligned} x^4-4x^2 &= 1&& \text{move all terms to the left hand side } \\[1 em]x^4-4x^2-1 &= 0&& \\[1 em] \end{aligned} $$
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas
This page was created using
Polynomial Equations Solver