Answer 1

x⁴ – 2x² – 3 = 0

`=> x^4 - 3x^2 + x^2 - 3 = 0`

`=> x^2(x^2 - 3) + 1(x^2 - 3) = 0`

`=> (x^2 - 3)(x^2 + 1) =0`

If `x^2 - 3 = 0` or `x^2 + 1 = 0`

then `x^2 = 3` or `x^2 = -1` (reject)

`=> x = +- sqrt3`