Question

solve for x
x^4-8x^2-9=0

Answer 1

x=i,-i,3,-3

Answer 2

thanks how did you find the answers

Answer 3

let u=x^2
so u^2=x^4
u^2-8u-9=0
(u+1)(u-9)=0
u=-1
u=9
remember u=x^2
x^2=-1 implies x=plus or minus i
x^2=9 imples x=plus or minus 3