Here is a YouTube video about Michael Ossman Teaches Complex Numbers for DSP, and is part of a growing collection of videos I have found to be useful. The reason is understanding how complex or imaginary numbers are used in DSP mathematics and understanding science related to software defined radio.
This tutorial, "Michael Ossman Teaches Complex Numbers for DSP" is free education you can watch, which will help you deepen your knowledge and be better prepared for licence exams, schoolwork, or operating radio equipment.