[tex]y=0\\\\
x^4-8x^2+16 = 0\\\\
(x^2)^2 - 2\cdot 4 \cdot x^2 + 4^2 = 0\\\\
(x^2 - 4)^2 = 0\\\\
(x^2 - 4)(x^2 - 4)=0\\\\
(x-2)(x+2) (x-2)(x+2) = 0\\\\
(x-2)(x-2) (x+2)(x+2) = 0\\\\
\Longrightarrow~~~ x_1 = 2;~x_2 = 2;~ x_3= -2;~x_4 = -2\\\\
\text{Conclusion:}\\\\
x_1 = x_2 = 2~~~ \text{double root}\\\\
x_3 = x_4 = -2~~~ \text{double root}\\\\
[/tex]
