I/Q is really amazing and it's an offshoot of the Euler's formula.

The best book to understand I/Q if your background is not engineering is probably this book "Digital Signal Processing in Modern Communication System" by Andreas Schwarzinger [1].

This book will teach from the basic principles of communication from the I/Q up to OFDM, basically most of the essential techniques of modern communication as mentioned in its title.

[1]https://www.amazon.com/Digital-Signal-Processing-Communicati...