If you don't like dealing with imaginary numbers, another approach is to just divide x2+2x+3 into x10 + ax5 + b. I haven't actually done it, but you will wind up with a remainder in the form of
(e + af)*x + (g + ah + b).
Set each of these equal to 0, giving a = -e/f and b = -g +he/f
Another approach
