[tex]x^4-10x^2=-9
[/tex]
[tex]x^4-10x^4+9=0[/tex]
Let [tex]x^2[/tex] be [tex]A[/tex]
Therefore,
[tex]A^2-10A+9=0[/tex]
Through quadratic factoring,
[tex](A-9)(A-1)=0[/tex]
[tex]A=1,9[/tex]
Resubstitute for [tex]x[/tex].
[tex]x^2=1[/tex]
[tex]x=1,-1[/tex]
and,
[tex]x^2=9[/tex]
[tex]x=3,-3[/tex]
