Complex solutions happen when the parabola does not touch the x-axis, or when x does not have a real solution for when y = 0. The process for solving is the same, the only difference will be that you will have to take the square root of a negative value which results in a complex solution.
Below are two worked examples. If you need to see an example there is a video link.
Below are two worked examples. If you need to see an example there is a video link.