Answer
$$ n=3\pm\sqrt2i$$
Work Step by Step
For imaginary numbers, we know that standard form is $a\pm bi$, where $a$ is the real part and $b$ is the imaginary part. To get the expression into this form, we combine like terms like we did with polynomials. Doing this, we find:
$$(n-3)^2=-2 \\ n-3 =\pm \sqrt2i \\ n=3\pm\sqrt2i$$