To solve the equation \( x^2 + 4 = 0 \), we can rearrange it to find \( x^2 = -4 \).
Taking the square root of both sides, we have:
\[ x = \pm \sqrt{-4} = \pm 2i \]
Where \( i \) is the imaginary unit.
Thus, the solutions for \( x \) are \( 2i \) and \( -2i \), which are both imaginary numbers.
So, the correct response is:
imaginary