X ^ 4 + 1 is decomposed into irreducible polynomials over the rational field

X ^ 4 + 1 is decomposed into irreducible polynomials over the rational field

It can only be divided on the field of real numbers
x^4+1
=x^4+2x^2+1-2x^2
=(x^2+1)^2-2x^2
=(x^2+2^(1/2)x+1)(x^2-2^(1/2)x+1)
Irreducible on rational number field (can be proved by Eisenstein's criterion)