虚数其实是真实存在的（第1部分：入门）

The first part of Welch Labs' series on imaginary numbers, presenting them as the natural extension of the number line into two dimensions. It covers the history and the math with strong visuals.

Why HN likes it: HN commenters rate the series as some of the best visual teaching on complex numbers and recommend it for building intuition.

“The greatest audiovisual content on the topic I have ever seen”