https://betterexplained.com/articles/a-visual-intuitive-guide-to-imaginary-numbers/

A really wonderful explanation of ‘i’, and the imaginary numbers in general. It’s difficult to understand the amazingly strange and important qualities of i and the imaginary numbers.

Particularly important is the idea of the √-1. A really fascinating mathematical … process. An operation, rather than merely a number….

https://betterexplained.com/articles/a-visual-intuitive-guide-to-imaginary-numbers/