I think you are doing the right thing. Just one word: since , are imaginary numbers.
For x^4 - 8x^2-4= 0 ,
Does x work out to be = +/-√(4+/-2√5)
N.B. +/- means + or -
I've subbed in my answer but it doesnt seem to work. I've tried finding x using quadratic formula and completing the square.
Can anyone please help?