OK, the solutions you have took a less-than-ideal approach. It'll work, but it relies on working with complex numbers more than is necessary. When you work with factors of i, it greatly increases your chance of making sign mistakes, so if you can avoid working with them, it's usually for the best. Also, the solutions evaluated the roots numerically too early. it's usually not a good idea to evaluate numerical expressions midway through the problem because you end up with decimals, like 3.969, that you have to copy from line to line and sometimes you drop a digit or transpose two of them, etc. It's just asking to make a mistake. Plus, like any time you plug numbers in too early, it obscures possible cancellations down the road.
Anyway, back to your problem... You made one other mistake. You did something like
\frac{a}{x+iy} \rightarrow \frac{a}{x}+i\frac{a}{y}
which isn't correct. What you need to do is multiply the top and bottom by the complex conjugate of the denominator, so you get
\frac{a}{x+iy} = \frac{a}{x+iy}\times\frac{x-iy}{x-iy} = \frac{a(x-iy)}{x^2+y^2} = \frac{ax}{x^2+y^2} - i\frac{ay}{x^2+y^2}
