x^4 + 2x^2 + 1 = 0

Question

(x^2)^2 +2x^2 +1 = 0
(x^2 + 1)^2 = 0
I don't know where to go now although I know the answer is
x = i, -i

Answer 1

x^2+1=0

x^2=-1 in real numbers it cant be.

so x=i and x=-i (solution in the set of complex numbers)