Here is a YouTube video about Michael Ossman Introduces Complex Numbers for Signal Processing, and is part of a growing collection of videos I have found to be useful. The reason is introductory understanding of complex numbers used for SDR radio signal processing and understanding science related to software defined radio.
This tutorial, "Michael Ossman Introduces Complex Numbers for Signal Processing" 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.