Step-by-step explanation:
Let u=x^2.
Notice that
[tex] {x}^{4} - 9 {x}^{2} + 8 = 0[/tex]
[tex]( {x}^{2} ) {}^{2} - 9( {x}^{2} ) + 8 = 0[/tex]
[tex]u {}^{2} - 9u + 8 = 0[/tex]
[tex](u - 8)(u - 1) = 0[/tex]
[tex]u = 8[/tex]
[tex]u = 1[/tex]
Replace x^2= u
[tex] {x}^{2} = 8[/tex]
[tex]x = ±2 \sqrt{2} [/tex]
[tex] {x}^{2} = 1[/tex]
[tex]x = ±1[/tex]
So our answer is
[tex]±1 \: [/tex]
and
[tex]±2 \sqrt{2} [/tex]
