9x^-4-35x^-2-4=0

Answer 1

I assume we are solving?

multiply each term by x^4

9 - 35x^2 - 4x^4 = 0
4x^4 + 35x^2 - 9 = 0
(x^2 +9)(4x^2 - 1) = 0
x^2 = -9 or x^2 = 1/4
x = ± 3i or x = ± 1/2

Answer 2

let z = x^-2
then z^2 = x^-4
9 z^2 - 35 z - 4 = 0
(9z+1)(z-4) = 0
z = 4 or z = -1/9
you take it from there