Here we relate many of the ideas from the last video. We talk about how we can think of sine and cosine as the sum of 2 circular motion terms in the complex plane and how those terms work to make sure sine cosine remain real. Then we talk about how engineers view the complex exponential as the most fundamental function since it only involves 1 frequency component, while sine and cosine involve 2 frequency components (in the complex plane!).
![](https://i.ytimg.com/vi/XtFGg640x9o/mqdefault.jpg)