Irreducible polynomials

RTH001
If i have to show a polynomial x^2+1 is irreduceable over the integers, is it enough to show that X^2 + 1 can only be factored into (x-i)(x+i), therefore has no roots in the integers, and is subsequently irreduceable?

Strictly speaking, because the problem said "irreduceable over the integers", it is because there are no integers satisfying $x^2+1= 0$. Of course, since the integers are a subset of the real numbers yours is a sufficient answer. But your teacher might call your attention to the difference by (on a test, perhaps) asking you to show that $x^2- 2$ is irreduceable over the integers.