Question 8086
hope this question is x^4-2x^2-8 =0

let x^2 be y .
Then,

y^2-2y-8=0
y^2-4y+2y-8=0
y(y-4)+2(y-4)=0
(y+2)(y-4)=0

----- > y=-2 or y=4
----- > x^2= -2 or x^2 = 4
----- > x= sqr root of -2 or x = +/-(plus or minus)2.